Laser device and exposure method

ABSTRACT

A laser device which can be used as a light source for an exposure device, can be downsized, and is easy to maintain. A laser beam (LB 6 ) emitted from a DFB (Distributed feedback) semiconductor laser, for example, and amplified by an optical fiber amplifier is passed through non-linear optical crystals ( 502, 503, 504 ) to be sequentially doubled in frequency to thereby generate an ultraviolet-region laser beam (LB 5 ) consisting of an octuple wave. A GdYCOB, that is, Gd x Y 1−x Ca 4 O(BO 3 ) 3  crystal (0≦×≦1) is used for the non-linear optical crystal ( 503 ) for a double wave-to-quadruple wave conversion, and a KAB, that is, K 2 Al 2 B 4 O 7  crystal for the non-linear optical crystal ( 504 ) for a quadruple wave-to-octuple wave conversion. The non-linear optical crystals ( 502-504 ) are all fine-tuned in phase match angle by temperature controllers ( 521-523 ) respectively.

This application is the international phase under 35 U.S.C. 371 of priorPCT International Application No. PCT/JP00/06131 which has anInternational filing date of Sep. 8, 2000 which designated the UnitedStates of America, the entire contents of which are hereby incorporatedby reference.

TECHNICAL FIELD

The present invention relates to a laser device that generatesultraviolet light and an exposure method using this device. Morespecifically, the present invention is preferably used as, for example,an exposure light source or a measuring light source of an exposureapparatus used in a photolithography process for manufacturingmicrodevices, such as semiconductor devices, image pickup devices (suchas CCDs), liquid crystal display devices, plasma display devices, andthin-film magnetic heads.

BACKGROUND ART

For example, an exposure apparatus used in a photolithography processfor manufacturing a semiconductor integrated circuit optically reducesand projectively exposes a circuit pattern accurately rendered on areticle (photomask) used as a mask, onto the photoresist-coated surfaceof a wafer as a substrate. In the exposure, shortening of anexposure-light wavelength (exposure wavelength) is one of the mostsimple and effective methods to reduce the minimum pattern size(resolution) on the wafer. Hereinbelow, a description will be maderegarding conditions that should be provided to configure an exposurelight source, in addition to those for the implementation of thewavelength shortening of the exposure-light.

First, for example, an optical output of several watts is required. Theoptical output is required to reduce time necessary for exposure andtransfer of an integrate circuit pattern and thereby to increase athroughput.

Second, when the exposure light is ultraviolet light having a wavelengthof 300 nm or shorter, an optical material which can be used for areflector member (lens) of a projection optical system is limited, andhence the difficulty increases for compensation of the chromaticaberration. For this reason, monochromaticity of the exposure light isrequired, and the spectral linewidth needs to be controlled to be about1 pm or less.

Third, the timelike coherence increases in association with thereduction in the spectral linewidth. As such, when light having a narrowspectral linewidth (wavelength width) is emitted as it is, anunnecessary interference pattern called “speckle” is generated.Therefore, in the exposure light source, the spatial coherence needs tobe reduced to suppress generation of the speckles.

One of conventional short-wavelength light sources satisfying theseconditions is a light source using an excimer laser in which the laseroscillation wavelength itself is a short wavelength. Anotherconventional short-wavelength light source is of a type using harmonicwaves generation of an infrared or visible-range laser.

A KrF excimer laser (having a wavelength of 248 nm) is used as theabove-described former short-wavelength light source. Currently, anexposure light source using a shorter-wavelength ArF excimer laser(having a wavelength of 193 nm) is under development. In addition, aproposal has been made for use of an F₂ laser (having a wavelength of157 nm), which is one of excimer lasers. However, these excimer lasersare of a large scale, and the oscillatory frequency thereof is at abouta level of several kHz in a present stage. This requires a per-pulseenergy to be increased to increase a per-unit-time radiation energy.This arises various problems. For example, the transmittance of anoptical component tends to vary because of so-called compaction and thelike, complicated maintenance is required and costs are increased.

As the aforementioned latter method, there is a method that uses asecondary nonlinear optical effect of a nonlinear optical crystal, andthereby converts long wavelength light (infrared light or visible light)into ultraviolet light of short wavelength. For example, a publication(“Longitudinally diode pumped continuous wave 3.5W green laser”, L. Y.Liu, M. Oka, W. Wiechmann and S. Kubota; Optics Letters, vol. 19,p189(1994)) discloses a laser source that performs a wavelengthconversion of light emitted from a solid-state laser excited by asemiconductor laser beam. The publication regarding the aforementionedconventional example describes a method of performing a wavelengthconversion for a 1,064-nm laser beam generated by an Nd:YAG laser byusing a nonlinear optical crystal, and thereby generates light of a4th-harmonic-wave of 266-nm. The solid-state laser is a generic name oflasers using a solid-state laser medium.

In addition, for example, Japanese Patent Application Laid-Open No.8-334803 and corresponding U.S. Pat. No. 5,838,709 proposed an arraylaser. The array laser is formed to include a plurality of laserelements in a matrix form (for example, a 10×10 matrix). Each of thelaser elements is formed to include a laser-beam generating sectionincluding a semiconductor laser, and a wavelength conversion section forperforming wavelength conversion for light emitted from the laser-beamgenerating section into ultraviolet light by using a nonlinear opticalcrystal.

The conventional array laser thus constituted enables an overall-devicelight output to be a high output while mitigating light outputs of theindividual laser elements to be lower. This enables burden onto theindividual nonlinear optical crystals to be lessened. On the other hand,however, since the individual laser elements are independent of oneanother, to apply the lasers to an exposure apparatus, oscillatoryspectra of the overall laser elements need to be set identical with oneanother at the overall width up to a level of 1 pm.

For the above reason, for example, the length of a resonator of each ofthe laser elements needs to be adjusted, or a wavelength-selectingdevice needs to be inserted into the resonator to cause the laserelement to autonomously oscillate with the same wavelength in a singlelongitudinal mode. In this connection, these methods arises otherproblems. For example, the aforementioned adjustment requires asensitive arrangement; and in proportion to the increase in theconstituent laser elements, the complexity of the configuration needs tobe increased to cause the overall devices to oscillate with the samewavelength.

On the other hand, known methods of actively unifying the wavelengths ofthe plurality of lasers include an injection seed method (for example,see, “Walter Koechner; Solid-state Laser Engineering, 3rd Edition,Springer Series in Optical Science, Vol.1, Springer-Verlag, ISBN0-387-53756-2, pp.246-249”). According to this method, light from asingle laser light source having a narrow spectral linewidth is splitinto a plurality of laser elements, and the laser beams are used asinduction waves to tune the individual laser elements, and in addition,to causes the spectral linewidths to be narrow bandwidths. However, themethod has problems in that it requires an optical system for separatingthe seed light into the individual laser elements and anoscillatory-wavelength tuning control section, thereby increasecomplexity of the configuration.

In addition, the array laser as described above enables the overalldevice to be significantly smaller than that with the conventionalexcimer laser, it still causes difficulty in packaging so as to reducethe diameter of overall arrayed output beams to several centimeters orsmaller. The array laser thus configured has additional problems. Forexample, each of the arrays requires the wavelength conversion section,thereby increasing the cost. In addition, suppose misalignment hasoccurred in a part of the laser elements constituting the array, ordamage has occurred with the constituent optical elements. In this case,the overall array needs to be once disassembled, the defective part ofthe laser elements needs to be taken out for repair, and the array needsto be reassembled after repair.

In view of the above, a primary object of the present invention is toprovide a laser device that can be used for a light source of theexposure apparatus, that enables the exposure apparatus to beminiaturized, and that enables the maintainability to be enhanced.

A second object of the present invention is to provide a laser devicethat enables the oscillatory frequency to be increased, and enables thespatial coherence to be reduced, as well as enabling the overalloscillatory spectral linewidth to be narrowed with a simpleconfiguration.

Additional object of the present invention is to provide an exposingmethod using such a laser divice as an exposure light source, anexposure apparatus that is compact and that has high flexibility, and anefficient manufacturing method of the aforementioned exposure apparatus.

DISCLOSURE OF THE INVENTION

Each of the laser devices of the present invention basically generatesultraviolet light and includes a laser light generator section whichgenerates mono-wavelength laser light in a wavelength range of from aninfrared region to a visible region; an optical amplifier sectionincluding an optical fiber amplifier which amplifies the laser lightgenerated by the laser light generator section; and a wavelengthconversion section which performs wavelength conversion of the laserlight amplified by the optical amplifier section into ultraviolet lightby using a nonlinear optical crystal.

The laser divice in each of the above-described aspects of the presentinvention allows use of a light source which is small and which has anarrow oscillatory spectrum such as, for example, a distributed feedback (DFB) semiconductor laser controlled in oscillation wavelength or afiber laser. High-output mono-wavelength ultraviolet light which has anarrow spectral width can be obtained in the following manner. Amono-wavelength laser beam output from the laser generator section isamplified using the optical fiber amplifier; and thereafter, the laserlight is converted into ultraviolet light through the nonlinear opticalcrystal. As such, the present invention enables the provision of thelaser device which is small and which has high maintainability.

In this case, for example, one of the following amplifiers can be usedfor the optical fiber amplifier: an erbium(Er)-doped fiberamplifier(EDFA), a ytterbium(Yb)-doped fiber amplifier(YDFA), apraseodymium(Pr)-doped fiber amplifier(PDFA), and a thulium(Tm)-dopedfiber amplifier (TDFA).

Concerning the configuration of the wavelength conversion section of thepresent invention, ultraviolet light formed of a harmonic wave having afrequency of an arbitrary integer multiple (a wavelength of an integerdivision of 1) with respect to that of the fundamental wave can beeasily output through combination of second-order harmonic generation(SHG) by a plurality of nonlinear optical crystals and sum frequencygeneration (SFG). In this case, the conversion efficiency needs to beincreased as high as possible.

In a first laser device of the present invention, wavelength conversionsection includes a plurality of nonlinear optical crystals which performwavelength conversion for the laser light amplified by the opticalamplifier section, and a plurality of temperature controller whichrespectively perform temperature control for the plurality of nonlinearoptical crystals to tune the phase matching angle at the time ofwavelength conversion. By tuning (such as final finetuning) of the phasematching angles of all nonlinear crystals by performing the temperaturecontrol, the conversion efficiency can be improved by the simplecontrol. In addition, when the phase matching for wavelength conversionis performed through the temperature control of the crystals,non-critical phase matching (NCPM) can be employed. Use of the NCPMoffers the advantage of not causing so-called “walk-off”, which refersto angle deviation between a fundamental wave and a harmonic wavethereof in a nonlinear optical crystal. In addition, the acceptanceangle in phase-matching angle is larger in value by about two digits. Assuch, a large alignment error tolerance can be set, and therefore themanufacture/assembly is facilitated.

In a second laser device of the present invention, a lithium tetraborate(Li₂B₄O₇) crystal (i.e., an LB4 crystal) is used for at least one of aplurality of nonlinear optical crystals in the wavelength conversionsection. The LB4 crystal is used, particularly for a portion whichgenerates an eighth-order harmonic wave as ultraviolet light from afundamental wave and a seventh-order harmonic wave thereof according tosum frequency generation. Thereby, high conversion efficiency can beobtained, and the laser device is imparted with anti-ultraviolet lightdurability.

In a third laser device of the present invention, a K₂Al₂B₄O₇ crystal(i.e., a KAB crystal) is used for at least one of the plurality ofnonlinear optical crystals in the wavelength conversion section. The LB4crystal is used, particularly for a portion which generates aneighth-order harmonic wave as ultraviolet light from a fundamental waveand a seventh harmonic wave thereof according to sum frequencygeneration, or the KAB crystal is used for a portion which generates theeighth-order harmonic wave as ultraviolet light from a fourth-orderharmonic wave thereof according to second-order harmonic generation.Thereby, high conversion efficiency can be obtained.

In a fourth laser device of the present invention, aGd_(x)Y_(1−x)Ca₄O(BO₃)₃ crystal (i.e., a GdYCOB crystal) is used for atleast one of the plurality of nonlinear optical crystals in thewavelength conversion section. The GdYCOB crystal is used, particularlyfor a portion which generates a fourth-order harmonic wave from asecond-order harmonic wave. In this case, a value (0≦×≦1) of theparameter x, which represents a composition, is adjusted to adjust anindex of double reflection, thereby imparting the crystal with thecapability of generating a fourth-order harmonic wave according to thenon-critical phase matching (NCPM). Thereby, angle deviation “walk-off”can be controlled not to occur between the fundamental wave(second-order harmonic wave) and the harmonic wave (fourth-orderharmonic wave) in the nonlinear optical crystal, and therefore agenerated harmonic wave maintains the same symmetry as that of theincident light. For this reason, when, for example, a seventh-orderharmonic wave is generated from a fourth-order harmonic wave and athird-order harmonic wave in a subsequent stage, a high conversionefficiency can be obtained without complicated beam compensation beingperformed for matching the beam shapes of the two.

A fifth laser device of the present invention generates ultravioletlight and includes a laser light generator section which generatesmono-wavelength laser light in a wavelength range of from an infraredregion to a visible region, an optical amplifier section including anoptical fiber amplifier which amplifies the laser light generated by thelaser light generator section, and a plurality of relay optical systemswhich performs wavelength conversion for the laser light amplified bythe optical amplifier section into ultraviolet light by using aplurality of nonlinear optical crystals and which relay the laser lightamong the plurality of nonlinear optical crystals, wherein the pluralityof relay optical systems are each disposed to allow light of onewavelength to pass through.

In this case, since single-wavelength light is passed through each ofthe relay optical systems, chromatic-aberration compensation isfacilitated, and the conversion efficiency is therefore improved. In theabove-described configuration, preferably, the wavelength conversionsection generates the eighth-order harmonic wave from the fundamentalwave and the seventh-order harmonic wave thereof, and uses the sumfrequency generation of two light beams of fundamental, second-orderharmonic, fifth-order harmonic, and sixth-order harmonic waves togenerate the seventh-order harmonic wave. In this case, when generating,for example, a seventh-order harmonic wave having a wavelength of 221nm, the wavelength conversion section avoids the necessity of using aβ-BaB₂O₄ crystal (BBO crystal), thereby improving the durability of thewavelength conversion section. On the other hand, however, whengenerating a seventh-order harmonic wave from third-order andfourth-order harmonic waves, the wavelength conversion section needs touse the BBO crystal which easily absorbs the seventh-order harmonicwave. In this case, a case can occur in which the durability is reduced.

A sixth-order laser device of the present invention generatesultraviolet light and includes a laser light generator section whichgenerates a mono-wavelength laser light in a wavelength range of from aninfrared region to a visible region, an optical amplifier sectionincluding an optical fiber amplifier which amplifies the laser light,and a wavelength conversion section which performs wavelength conversionfor the amplified laser light into ultraviolet light having a wavelengthof about 200 nm or shorter by using a plurality of nonlinear opticalcrystals, wherein one of lithium tetraborate and KAB crystals is usedfor the last stage nonlinear optical crystal of the plurality ofnonlinear optical crystals which generates the ultraviolet light.

Preferably, each of the above-described laser devices is configured tofurther include an optical splitting section which splits the laserlight generated by the laser light generator section into a plurality oflaser beams, and, in this configuration, optical amplifier sections areindependently provided for the plurality of split laser beamsrespectively, and the wavelength conversion section collects fluxes oflaser beam output from the plurality of optical amplifier sections andperforms wavelength conversion thereof. Thus, the laser beams split bythe optical splitters are sequentially imparted with predetermineddifferences in optical-path lengths, and therefore, the spatialcoherence of the laser beams finally bundled can be reduced. Moreover,since each of the laser beams are generated by the common laser lightgenerator section, the spectral linewidth of the finally obtainedultraviolet light is narrow.

A seventh laser device of the present invention generates ultravioletlight and includes a laser light generator section which generates amono-wavelength laser light in a wavelength range of from an infraredregion to a visible region, an optical splitter section which splits thelaser light generated by the laser generator section into a plurality ofluminous fluxes, a plurality of optical amplifier sections whichamplifies each of the plurality of luminous fluxes split by the opticalsplitter section by using optical fiber amplifiers, and a wavelengthconversion section which performs wavelength conversion of laser lightof a bundle of the plurality of luminous fluxes from the plurality ofoptical amplifier sections into ultraviolet light by using a pluralityof nonlinear optical crystals, wherein the wavelength conversion sectionincludes a nonlinear crystal which generates a harmonic wave accordingto sum frequency generation of a first beam composed of a fundamentalwave or a harmonic wave of the laser light and a second beam composed ofa harmonic wave of the laser light, and an anisotropic optical systemhaving magnifications which are different in two directions crossingwith each other to match the individual magnitudes of the plurality ofluminous fluxes composing the first beam to the individual magnitudes ofthe plurality of luminous fluxes composing the second beam.

According to the above-mentioned present invention, the laser device canbe formed to be small and to have high maintainability, and in addition,the spatial coherence of the laser beams finally bundled can be reduced.Moreover, since each of the laser beams are generated by the commonlaser light generator section, the spectral linewidth of the finallyobtained ultraviolet light is narrow.

In addition, “walk-off” occurs because of crystal birefringence in thewavelength conversion section when angle-wise phase matching isperformed through wavelength conversion. In this case, the output beamis shaped as an asymmetric ellipse. When the output beam is used aslight to be incident on a subsequent nonlinear optical crystal, the beamneeds to be shaped to improve the conversion efficiency. As such, anoptical system having different magnifications in the longitudinal andtransverse directions is used in the course of beam shaping. In anexample configuration performing five-stage wavelength conversion for193-nm generation, “walk-off” can occur in fourth-order harmonic wavegeneration and seventh-order harmonic wave generation. As such, theexample configuration uses an optical system, such as a cylindrical lenspair, which has different magnifications in the longitudinal andtransverse directions. In this case, however, while the beam shape ofeach of the plurality of luminous fluxes forming a bundle (bundle of theplurality of luminous fluxes) is shaped, the shape of the overall bundleis deformed according to magnifications corresponding to themagnifications in the longitudinal and transverse directions of the lenssystem being used.

For example, in a case where a fourth-order harmonic wave output isshaped using an optical system having different magnifications in thelongitudinal and transverse directions, the beams of the fourth-orderharmonic wave and the third-order harmonic wave need to be overlappedwith each other in the subsequent seventh-order harmonic wavegeneration. Beam-overlapping for two luminous fluxes requires that thepositions of individual beams in a bundle are matched, and the beams aresatisfactorily overlapped with each other. When the fourth-orderharmonic wave is shaped using the optical system having differentmagnifications in the longitudinal and transverse directions, also theoverall shape of the bundle itself is deformed according tomagnifications corresponding to the magnifications in the longitudinaland transverse directions of the lens systems being used. On the otherhand, since the shape of the bundle of the third-order harmonic wave andthe individual beam shapes are different from that of the fourth-orderharmonic wave, the two need to be simultaneously tuned. As such, themagnification of the optical system for shaping the bundle and themagnification of the optical system for shaping the individual beam needto be set independently of each other. Because of the above, ananisotropic optical system having different magnifications depending onthe longitudinal and transverse directions of each of the beams isconcurrently used in addition to an ordinary cylindrical-lens pair or acombination of a lens and a cylindrical lens. Thereby, the ratio of anoverlapped portion of the two beams is maximized, and high conversionefficiency can be obtained. Usable examples of the anisotropic opticalsystem include a cylindrical-lens array, a prism array, and a DOE(diffractive optical element) in which fine diffraction gratings aredistributed in a predetermined arrangement.

The anisotropic optical system is preferably inserted either on theoptical path of the fundamental wave in the wavelength range of from aninfrared region and a visible region or on an optical path of a harmonicwave of a low order (such as a third or fourth order). These wavelengthsoffer a high degree of freedom in optical-material selection, therebyenabling appropriate optical materials to be selectable.

Furthermore, in the present invention, the laser beam can be modulatedby a light modulator and the like at a high frequency of, for example,about 100 kHz. As such, in comparison to a case where an excimer laserlight (having a wavelength of several kHz) is used, the pulse energy canbe reduced to about 1/1000 to 1/10000 to obtain the same illuminance.Therefore, when the above-described laser device is used as an exposurelight source, transmittance variations due to, for example, compaction,can substantially be eliminated, and stable and high-accuracy exposurecan be implemented.

For example, ultraviolet light substantially having the same wavelengthof 193 to 194 nm as that of an ArF excimer laser can be obtained in aconfiguration in which a laser beam whose wavelength is limited to 1.5μm, particularly to a range of from 1.544 to 1.552 μm is irradiated fromthe laser light generator section, and the eighth-order harmonic wave ofthe fundamental wave thereof is generated in the wavelength conversionsection. Moreover, ultraviolet light substantially having the samewavelength of 157 to 158 nm as that of an F₂ laser can be obtained in aconfiguration in which a laser beam whose wavelength is limited to near1.5 μm, particularly to a range of from 1.57 to 1.58 μm is irradiatedfrom the laser light generator section, and the tenth-order harmonicwave of the fundamental wave thereof is generated in the wavelengthconversion section. Similarly, ultraviolet light substantially havingthe same wavelength as that of an F₂ laser can be obtained in aconfiguration in which a laser beam whose wavelength is limited to near1.1 μm, particularly to a range of from 1.099 to 1.106 μm is irradiatedfrom the laser light generator section, and the seventh-order harmonicwave of the fundamental wave thereof is generated in the wavelengthconversion section.

Moreover, in the exposure method of the present invention ultravioletlight from the laser device of the present invention is incident onto amask, and a substrate is exposed with the ultraviolet light passedthrough a pattern of the mask. The exposure apparatus of the presentinvention uses the laser divice of the present invention as an exposurelight source, and includes an illumination system which irradiate a maskwith ultraviolet light from the laser device, and a projection opticalsystem which projects an image of a pattern of the mask onto asubstrate, wherein the substrate is exposed with the ultraviolet lightpassed through the pattern of the mask. With the laser device of thepresent invention being used, the exposure apparatus can be miniaturizedoverall, and the maintainability thereof is increased.

Moreover, a manufacturing method of the exposure apparatus of thepresent invention is a method of manufacturing an exposure apparatuswhich illuminates the mask with the ultraviolet light, and which exposesa substrate with the ultraviolet light passed through a pattern of themask, wherein the laser device of the present invention is used as anexposure light source, and the laser device, an illumination systemwhich irradiates a mask with ultraviolet light from the laser device,and a projection optical system which projects an image of a pattern ofthe mask onto a substrate, are disposed to have a predeterminedrelationship.

BRIEF DESCRIPTION OF THE FIGURES IN THE DRAWINGS

FIGS. 1A and 1B are diagrams showing an example of an ultraviolet lightgenerator according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration example of optical amplifierunits 18-1 to 18-n shown in FIGS. 1A and 1B.

FIG. 3A is a diagram showing a first configuration example of awavelength conversion section 20 shown in FIGS. 1A and 1B, and FIG. 3Bis a diagram showing a second configuration example of the wavelengthconversion section 20.

FIG. 4 is a diagram showing a third configuration example of thewavelength conversion section 20.

FIG. 5 is a diagram showing a state where a third-order harmonic waveand a fourth-order harmonic wave overlap with each other in aconfiguration not using an anisotropic converging lens in FIG. 4.

FIG. 6 is a diagram showing a state where the third-order harmonic waveand the fourth-order harmonic wave overlap with each other in awavelength conversion section shown in FIG. 4.

FIG. 7 is a configuration view showing a projection exposure apparatusincluding an example of an ultraviolet light generator of the embodimentof the present invention.

FIG. 8 is a diagram showing another configuration example of awavelength conversion section 20 of the present invention.

FIGS. 9A and 9B are diagrams showing a still another configurationexample of a wavelength conversion section 20 of the present invention.

FIGS. 10A and 10B are diagrams showing a still another configurationexample of a wavelength conversion section 20 of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, an example of a preferred embodiment according to thepresent invention will be described with reference to the accompanyingdrawings. The present example represents a configuration in which alaser device of the present invention is applied to an ultraviolet lightgenerator that can be used as an ultraviolet-region exposure lightsource of a projection exposure apparatus such as a stepper or as alight source for alignment and various tests.

FIG. 1A shows an ultraviolet light generator according to the presentexample. Referring to FIG. 1A, a mono-wavelength oscillatory laser 11,which is provided as a laser generator section, generates a laser beamLB I that is formed of, a continuous wave (CW) having a narrow spectralwidth and that has a wavelength of 1.544 μm. The laser beam LB1 isincident on an optical modulating device 12, which is provided as anoptical modulator, via an isolator IS1 provided for blocking reverselight. The laser beam LB1 is converted therein into a laser beam LB2(pulse beam), and the laser beam LB2 is then incident on an opticalsplitting amplifier section 4.

The laser beam LB2 incident on the optical division amplifier section 4passes through an optical fiber amplifier 13 provided as a front-stageoptical amplifier section, passes through the optical fiber amplifier13, and is amplified therethrough. The amplified beam is then incidenton a splitter 14 of a planar waveguide type provided as a first opticalsplitting device via an isolator IS2, and is then split into m laserbeams each having the same optical intensity. The letter m representsinteger “2” or a greater integer. In the present example, m=4. For theoptical fiber amplifier 13, the apparatus uses an erbium-doped fiberamplifier (EDFA) to amplify light having the same wavelength zone (whichis near 1.544 μm in the present example) as that of the laser beam LB1,which generated by the mono-wavelength oscillatory laser 11. Anexcitation beam having a wavelength of (980±10) nm or (1480±30) nm isfed into the optical fiber amplifier 13 via a coupling-dedicatedwavelength division multiplexing device (not shown). In the EDFA toprevent the increase in wavelength according to nonlinear effects, the(980±10) nm laser beam is preferably used as excitation beam to therebyreduce the fiber length. The above is the same for a rear-stage opticalfiber amplifier.

A (970±10) nm beam may be used as the excitation beam for either anytterbium(Yb)-doped fiber or an erbium/ytterbium-codoped fiber.

The m laser beams that have been output from the splitter 14 areincident on planar-waveguide-type splitters 16-1, 16-2, . . . , and 16-mindividually provided as second optical splitting devices via respectiveoptical fibers 15-1, 15-2, . . . , and 15-m each having a differentlength. Thereby, the m laser beams are each split into n laser beamseach having substantially the same optical intensity. The letter nrepresents “2” or a greater integer; and n=32 in the present example.The first optical splitting device (14) and the second optical splittingdevices (16-1 to 16-m) correspond to optical splitters of the presentembodiment according to the present invention. Consequently, the laserbeam LB1 emitted from the mono-wavelength oscillatory laser 11 is splitoverall into n·m laser beams (that is, 128 laser beams in the presentexample).

N laser beams LB3 output from the splitter 16-1 are incident on opticalamplifier units 18-1, 18-2, . . . , and 18-n, individually provided asrear-stage optical amplifier sections, via respective optical fibers17-1, 17-2, . . . , and 17-n each having a different length; and theincident beams are amplified therethrough. The optical amplifier units18-1 to 18-n each amplify a laser beam having the same wavelength zone(near 1.544 μm in the present example) as that of the laser beam LB1generated by the mono-wavelength oscillatory laser 11. Similar to theabove, n laser beams output from the other splitter 16-2 to 16-m areincident on optical amplifier units 18-1 to 18-n, individually providedas the rear-stage optical amplifier sections, via respective opticalfibers 17-1 to 17-n each having a different length; and the incidentbeams are amplified therethrough.

The laser beams amplified by the m-group optical amplifier units 18-1 to18-n propagate through extended portions of output terminals of opticalfibers (described below) doped with a predetermined matter in therespective optical amplifier units 18-1 to 18-n. The aforementionedextended portions form a fiber bundle 19. The lengths of the m-group noptical fibers forming the fiber bundle 19 are identical to one another.However, the configuration may be such that the fiber bundle 19 isformed bundling, and the laser beams amplified by the optical amplifierunits 18-1 to 18-n are transferred to the corresponding optical fibers.Thus, the optical splitting amplifier unit 4 is configured to includethe members provided between the optical fiber amplifier 13 and thefiber bundle 19. The configuration of the optical splitting amplifiersection 4 is not limited to that shown in FIGS. 1A and 1B. For example,a time division multiplexer may be used as an optical splitter.

Laser beams LB6 having been output from the fiber bundle 19 are incidenton a wavelength conversion section 20 including a nonlinear opticaldevice, and is converted thereby into laser beams LB5 each formed ofultraviolet light. The laser beams LB5 are output to the outside asalignment light or testing light. As described above, the m-groupoptical amplifier units 18-1 to 18-n are provided to individuallycorrespond to the optical amplifier sections of the present invention.However, a case may be in which the optical fibers in the fiber bundle19 are included in the optical amplifier sections.

Moreover, as shown in FIG. 1B, output terminals 19 a of the fiber bundle19 are bundled such that the m·n optical fibers (128 optical fibers inthe present example) tightly contacts one another, and the outer shapethereof is circular in a cross-sectional view. In a practicalconfiguration, however, the outer shape of the output terminals 19 a andthe number of optical fibers are determined according to, for example,the rear-stage configuration of the wavelength conversion section 20 anduse conditions of the ultraviolet light generator of the presentexample. The clad diameter of each of the optical fibers constitutingthe fiber bundle 19 is about 125 μm. Accordingly, when 128 opticalfibers are bundled circular, a diameter d1 of each of the outputterminals 19 a can be set to about 2 mm or smaller.

The wavelength conversion section 20 converts the incident laser beamLB6 to a laser beam LB5 formed of either an eighth-order harmonic wave(wavelength: 1/8) or a tenth-order harmonic wave (wavelength: 1/10). Thewavelength of the laser beam LB1 output from the mono-wavelengthwavelength oscillatory laser 11 is 1.544 μm. Accordingly, the wavelengthof the eighth-order harmonic wave is 193 nm, which is the same as thatof the ArF excimer laser; and the wavelength of the tenth-order harmonicwave is 154 nm, which is substantially the same as the wavelength (157nm) of the F₂ laser (fluorine laser). Suppose a case occurs in which thewavelength of the laser beam LB5 needs to be approximated closer to thewavelength of the F₂ laser. This case can be achieved such that thewavelength conversion section 20 is controlled to generate a tenth-orderharmonic wave, and in addition, the mono-wavelength oscillatory laser 11is controlled to generate a laser beam having a wavelength of 1.57 μm.

In practice, ultraviolet light substantially having the same wavelength(193 to 194 nm) as that of the ArF excimer laser can be obtained in sucha way that the oscillation wavelength of the mono-wavelength oscillatorylaser 11 is regulated to be in a range of from 1.544 to 1.552 μm, and isconverted to the eighth-order harmonic wave. Similarly, ultravioletlight substantially having the same wavelength (157 to 158 nm) as thatof the F₂ laser in such a way that the oscillation wavelength of themono-wavelength oscillatory laser 11 is regulated to be in a range offrom 1.57 to 1.58 μm, and is converted to the tenth-order harmonic wave.As such, these ultraviolet light generators can be used as inexpensiveand easily maintainable light sources in place of the ArF excimer lasersource and the F₂ laser source.

Alternative other methods may be employed instead of the method offinally obtaining the ultraviolet light having the wavelength that isclose to the wavelength zone of the ArF excimer laser or the F₂ laser.For example, in one of the alternative methods, an optimalexposure-light wavelength (for example, 160 nm, or the like) isdetermined according to patterning rules furnished for a manufacturingobject such as a semiconductor device; and, for example, the oscillationwavelength of the mono-wavelength oscillatory laser 11 and themagnification of harmonic waves in the wavelength conversion section 20are thereby determined so that ultraviolet light having a theoreticallyoptimum wavelength can be obtained. That is, the wavelength of the lightgenerated in the wavelength conversion section 20 may be arbitrary (forexample, about 200 nm or shorter), or may be different from theeighth-order and tenth-order harmonic waves; and the configuration ofthe wavelength conversion section 20 may be arbitrary.

Hereinbelow, the present embodiment will be described in further detail.Referring to FIG. 1A, for the mono-wavelength oscillatory laser 11oscillating at a single wavelength, the present example uses, a laser,such as a distributed feedback (DFB) semiconductor laser. The DFBsemiconductor laser is characterized by an InGaAsP construction, a 1.544μm oscillation wavelength, and a 20 mW continuous output (whichhereinbelow will be referred to as “CW output”). In addition, the DFBsemiconductor laser is configured such that, instead of a Fabry-Pelotresonator, a diffraction grating is formed in a semiconductor laser, inwhich single longitudinal mode oscillation is performed under anycondition. Thus, since the DFB semiconductor laser performs the singlelongitudinal mode oscillation, the oscillation spectral linewidth can becontrolled to be 0.01 pm or less. Alternatively, for the mono-wavelengthoscillatory laser 11, the present example may be configured using alight source such as an erbium(Er)-doped fiber laser capable ofgenerating a laser beam having a wavelength region similar to the aboveand a narrowed bandwidth.

In addition, the output wavelength of the ultraviolet light generator ofthe present example is preferably fixed to a specific wavelengthdepending on the usage. As such, the present example includes anoscillation wavelength controller provided to control the oscillationwavelength of the mono-wavelength oscillatory laser 11, provided as amaster oscillator, to be a predetermined wavelength. As in the presentexample, in the configuration using the DFB semiconductor laser for themono-wavelength oscillatory laser 11, the oscillation wavelength can becontrolled according to a method of controlling the temperature of theDFB semiconductor laser. This method enables, for example, theoscillation wavelength to be more stably controlled to be apredetermined wavelength, and the output wavelength to be finely tuned.

Ordinarily, a component such as the DFB semiconductor laser is providedover a heatsink, and the components are stored in a package. In thepresent example, a temperature regulator section 5 (which is formed of,for example, a heating device such as a heater, a heat absorbing devicesuch as a Peltier device, a temperature detecting device, and athermistor) is fixed to a heatsink attached to the mono-wavelengthoscillatory laser 11 (such as the DFB semiconductor laser). In thisconfiguration, operation of the temperature regulator section 5 iscontrolled by a control section 1 comprising a computer, and thetemperatures of the heatsink and the mono-wavelength oscillatory laser11 are thereby controlled with a high accuracy. For example, thetemperature in the DFB semiconductor laser can be controlled in units of0.001° C. Moreover, the control section 1 performs high-accuracy controlfor power (driving current in the DFB semiconductor laser) for drivingthe mono-wavelength oscillatory laser 11 via a driver 2.

The oscillation wavelength of the DFB semiconductor laser has atemperature dependency of about a 0.1 nm/° C. When the temperature ofthe DFB semiconductor laser is changed by, for example, 1° C., thewavelength is changed by 0.1 nm in the fundamental wave (wavelength:1544 nm). Accordingly, in the eighth-order harmonic wave (193 nm), thewavelength thereof is changed by 0.1 nm; and in the tenth-order harmonicwave (157 nm), the wavelength thereof is changed by 0.01 nm. When thelaser beam LB5 is used for the exposure apparatus, compensation needs tobe performed for, for example, errors that can occur according todifferences in atmosphere of environments where the exposure apparatusis placed or errors that can occur because of variations in imagingproperties. As such, preferably, the laser beam LB5 can preferably bevaried by about ±20 pm with respect to the central wavelength. This canbe implemented by changing the temperature of the DFB semiconductorlaser by about ±1.6° C. for the eighth-order harmonic wave and by ±2° C.for the tenth-order harmonic wave.

For a monitor wavelength used in feedback control when controlling theabove-described oscillation wavelength to be a predetermined wavelength,a wavelength that provides sensitivity necessary for desired wavelengthcontrol and that has high monitorablility may be selected frompost-wavelength-conversion harmonic-wave outputs (such as a second-orderharmonic wave, a third-order harmonic wave, and a fourth-order harmonicwave) in the wavelength conversion section 20 (described below). In anevent a 1.51-to-1.59 μm DFB semiconductor laser is used for themono-wavelength oscillatory laser 11, the third-order harmonic wave ofthe oscillation laser beam has a wavelength in a range of from 503 nm to530 nm. This wavelength band corresponds to a wavelength zone whereiniodine-molecule absorption lines are present at a high density. As such,even higher-accuracy wavelength control can be implemented in such a waythat an appropriate iodine-molecule absorption line is selected and islocked to the wavelength thereof. The present example is arranged suchthat a predetermined harmonic wave (preferably, the third-order harmonicwave) in the wavelength conversion section 20 is compared with theselected appropriate iodine-molecule absorption line (referencewavelength), and the differential amount of the wavelength is fed backto the control section 1. Then, based on the feedback, the controlsection 1 controls the temperature of the mono-wavelength oscillatorylaser 11 to cause the differential amount to become a predeterminedvalue. In this case, the control section 1 may be arranged such that theoscillation wavelength of the mono-wavelength oscillatory laser 11 ispositively controlled to vary, and the output wavelength thereof can betuned.

For example, in an exposure apparatus exposure light source to which theultraviolet light generator of the present example is applied, theformer method, described above, enables the prevention of aberrationfrom occurring with a projection optical system because of wavelengthvariations. Consequently, the method avoids variations in imagingproperties (optical properties such as image quality) to occur duringpattern transfer.

The latter method, described above, enables compensation for variationsin image properties (such as aberrations) of the projection opticalsystem. The variations can occur because of, for example, an elevationaldifference and an atmospheric difference between a manufacturing site,in which the exposure apparatus is assembled and tuned, and a placementsite (delivery site) of the exposure apparatus. The variations can alsooccur because of a difference in environments (such as inter-clean-roomatmospheres). This enables reduction in time required for installationof the exposure apparatus in the delivery site. Moreover, the lattermethod enables compensation for variations of various types that occurduring operation of the exposure apparatus. The variations include thosein aberrations with an illumination optical system, in projectionmagnification, and focal position. These variations can occur inassociation with changes in reticle illumination conditions(specifically, illuminant-energy distributions of exposure illuminationlight on a pupillary surface of an illumination optical system)according to irradiation of exposure illumination light, atmosphericvariations, and illumination optical systems. As such, the latter methodenables a pattern image to be transferred on a substrate always in thebest imaging condition.

The laser beam LB1, formed of continuous light output from themono-wavelength oscillatory laser 11, is converted into the laser beamLB2, formed of a pulse beam, by use of the optical modulating device 12.The optical modulating device 12 is formed of, for example, anelectrooptical modulating device or an acousto-optical modulatingdevice. The optical modulating device 12 is driven by the controlsection 1 through the driver 3. Hereinbelow, a description will be madewith reference to an example of the present example configuration inwhich the optical modulating device 12 performs the modulation into apulse beam characterized by a pulsewidth of 1 ns and a repetitionfrequency of 100 kHz (pulse cycle: 10 μs). As a result of the opticalmodulation, the peak output power of the pulse beam produced from theoptical modulating device 12 becomes 20 mW, and the average out putpower thereof becomes 2 μW. In the example case, no loss is assumed tooccur because of insertion of the optical modulating device 12. However,a loss of the insertion occurs in practice. For example, with a loss of−3 dB, the value of the peak output is thereby reduced to 10 mW, and thevalue of the average output is thereby reduced to 1 μW.

When using an electrooptical modulating device for the opticalmodulating device 12, the electrooptical modulating device is preferablyof a type (such as a two-electrode-type modulator) that has an electrodestructure subjected to chirp compensation. The aforementioned modulatoris preferably used to reduce the wavelength expansion of asemiconductor-laser output, which is caused by chirp occurring accordingto a timewise variation in the refractive index. In addition, in theoptical fiber amplifiers in the optical amplifier units 18-1 to 18-n,the amplification factor can be can be prevented from being reducedbecause of influence of ASE (amplified spontaneous emission) noise. Theabove prevention can be achieved by setting the repetition frequency toa level of 100 kHz or higher. Moreover, suppose the illuminance ofultraviolet to be finally output may be the same level as that of aconventional excimer laser beam (of which the pulse frequency is a levelof several kHz). In this case, as in the present example, the pulsefrequency is increased, and individual pulse beams are bundled into, forexample, an aggregate of 128 delayed pulse beams. Thereby, the per-pulseenergy can be reduced to a level of 1/1000 to 1/10000 to reducevariations, which can occur by compaction and the like, in refractiveindex of an optical member (such as a lens). For this reason, themodulator is preferably configured as described above.

Furthermore, a semiconductor laser or the like can be caused to generateoutput light through pulse oscillation by controlling the current of thelaser. As such, the present example preferably uses the current (power)control for the mono-wavelength oscillatory laser 11 (such as the DFBsemiconductor laser) and the optical modulating device 12 inassociation. The power control for the mono-wavelength oscillatory laser11 is performed to oscillate a pulse beam having a pulsewidth of, forexample, a level of 10 to 20 ns. Concurrently, the optical modulatingdevice 12 is used to take out a part of the pulse beam. Thus, thepresent example performs modulation into a pulse beam having apulsewidth of 1 ns.

In the above-described manner, the configuration of present example isenabled to easily generate the pulse beam with the narrower pulsewidth,in comparison to the configuration using only the optical modulatingdevice 12. In addition, the configuration of the present invention isenabled to more easily control, for example, the pulse-beam oscillationinterval, and activation and termination of the oscillation.Particularly, the associated use of the power control and themono-wavelength oscillatory laser 11 is preferable in a case where theextinction ratio is not high enough even when only the opticalmodulating device 12 is used to cause the pulse beam to be in the offstate.

The pulse beam output thus obtained is then coupled to the erbium-dopedoptical fiber amplifier 13 on the initial stage, and 35 dB (3162 times)amplification is performed thereby. At this stage, the pulse beam isamplified to have a peak output power of about 63 W and an averageoutput power of about 6.3 mW. In the above-described configuration, amultistaged optical fiber amplifier may be used to replace the opticalfiber amplifier 13.

The output of the initial-stage optical fiber amplifier 13 is firstparallely split using the splitter 14 into four outputs for channels 0to 3 (in the present example, m=4). Outputs of the respective channels 0to 3 are then couple to the optical fibers 15-1 to 15-4 having thelengths different from one another. Thereby, delay times correspondingto the optical fiber lengths are allocated for the outputs of theoptical fibers 15-1 to 15-4. For example, in the present embodiment, thepropagation rate of light in each of the optical fibers is assumed to be2×10⁸ m/s. The optical fibers 15-1 to 15-4 respectively having lengthsof 0.1 m, 19.3 m, 38.5 m, and 57.7 m are coupled to the channels 0, 1,2, and 3, respectively. In this case, the delay of light between theadjacent channels at an exit terminal of each of the optical fibers is96 ns. For the convenience of description, the optical fibers 15-1 to15-4 thus used for delaying the light are each called a “delay fiber”.

Subsequently, the outputs of the four delay fibers are further parallelysplit by the splitters 16-1 to 16-4 into 32 outputs (in the presentexample, n=32) (by each of the splitters for channels 0 to 31). That is,the outputs are split into the total of 4×32 (=128) channels. Then, therespective optical fibers 17-1 to 17-32 (delay fibers) each having adifferent length are coupled to output terminals of the channels 0 to 31to allocate a 3-ns delay time between the adjacent channels. That is, a93-ns delay time is allocated for the channel 31. On the other hand, the96-ns delay time is allocated for the first to fourth splitters 16-1 to16-4 at the time of input. Consequently, at output terminals of thetotal 128 channels provided overall, the pulse beam having the 3-nsdelay time between the adjacent channels can be obtained.

As a result of the above, the spatial coherence of the laser beam LB6,which is to be output from the fiber bundle 19, is reduced on the orderof 1/128, in comparison to a case where a cross-sectional shape of thelaser beam LB1 to simply be output from the mono-wavelength oscillatorylaser 11 is enlarged. As such, the present example exhibits an advantagein that the amount of speckles occurable when the finally obtainablelaser beam LB5 is used as exposure light is very small.

As described above, according to the splitting process and thedelay-time allocation, the present example enables the pulse beamshaving the 3-ns delay time between the adjacent channels to be obtainedat the output terminals of the total 128 channels. The pulse beamobserved at each of the output terminals has the same frequency of 100kHz (pulse cycle: 10 μs) as that of the pulse beam modulated by theoptical modulating device 12. Accordingly, in view of the overall lasergenerator section, repetition takes place at a cycle of 100 kHz suchthat 128 pulses are generated at 3-ns intervals, and a subsequent pulsetrain is then generated after an interval of 9.62 μs.

In the present embodiment, description has been made with reference tothe example in which the split number is 128, and the relatively shortdelay fibers are used. As such, a non-emission interval of 9.62 μsoccurs between the individual pulse trains. However, the pulse intervalscan be completely equalized in such a way that the split numbers m and nare increased, or appropriately longer delay fibers are used, or acombination thereof is employed.

According to the above, it can be viewed that a time divisionmultiplexing means (TDM means) is configured overall by the splitter 14,optical fibers 15-1 to 15-m, splitters 16-1 to 16-m, and m-group opticalfibers 17-1 to 17-n of the present example. In the present example, thetime division multiplexing means is configured of two stages of thesplitters. However, the time division multiplexing means may beconfigured of three or more stages of splitters; or alternatively, itmay be configured only of one stage of splitters while the split numberis reduced. Moreover, while the splitters 14 and 16-1 to 16-m are of aplanar waveguide type, the configuration may use splitters of adifferent type, such as fiver splitters or beam splitters using apartial transmission mirror.

In addition, the present example is capable of tuning the oscillationtiming, i.e., a repetition frequency f by controlling the timing of adriving voltage pulse applied to the optical modulating device 12.Moreover, in a case where output variations can occur with the pulsebeam according to a change in the oscillation timing, the arrangementmay be made such that the magnitude of the driving voltage pulse, whichis to be applied to the optical modulating device 12, is synchronouslytuned to compensate for the output variations. In this case, thearrangement may be such that the pulse-beam output variations arecompensated for only through the use of oscillation control of themono-wavelength oscillatory laser 11 or through the associated usethereof with the above-described control of the optical modulatingdevice 12.

Referring to FIG. 1A, the laser beams passed through the m-group delayfibers (optical fibers 17-1 to 17-n) are incident on the respectiveoptical amplifier units 18-1 to 18-n, and are amplified thereby. Theindividual optical amplifier units 18-1 to 18-n of the present examplehave optical fiber amplifiers. While description given hereinbelow willcover example configurations of an optical amplifier unit 18 that may beused for the optical amplifier unit 18-1, the example configurations maysimilarly be used for the other optical amplifier units 18-2 to 18-n.

FIG. 2 shows an optical amplifier unit 18. Referring to FIG. 2, theoptical amplifier unit 18 shown therein is basically configured toinclude two stages of optical fiber amplifiers 22 and 25 being coupled.The individual optical fiber amplifiers 22 and 25 are formed oferbium-doped fiber amplifiers (EDFAs). Two end portions of thefirst-stage optical fiber amplifier 22 are coupled to wavelengthdivision multiplexing devices 21A and 21B (each of which hereinbelowwill be referred to as a “WDM device”). The respective WDM devices 21Aand 21B feed an excitation beam EL1 and another excitation beamforwardly and backwardly to the optical fiber amplifier 22. Theexcitation beam EL1 is fed from a semiconductor laser 23A, provided as alaser light source; and the other laser beam is fed from a semiconductorlaser 23B, provided as a laser light source. Similarly, two end portionsof the second-stage optical fiber amplifier 25 are coupled tocoupling-dedicated WDM devices 21C and 21D. The respective WDM devices21C and 21D forwardly and backwardly feed excitation beams, fed fromsemiconductor lasers 23C and 23D, to the optical fiber amplifier 25.Thus, each of the optical fiber amplifiers 22 and 25 is of a two-wayexcitation type.

Each of the optical fiber amplifiers 22 and 25 amplifies light having awavelength in a range of, for example, from about 1.53 to 1.56 μm, whichis inclusive of the wavelength of the incident laser beam LB3 (in thepresent example, the wavelength thereof is 1.544 μm). A narrow bandfilter 24A and an isolator IS3 for blocking reverse light are disposedin a boundary portion between the optical fiber amplifiers 22 and 25,more specifically, between the WDM devices 21B and 21C. For the narrowband filter 24A, either a multilayer film filter or a fiber bragggrating may be used.

In the present example, the laser beam LB3 from the optical fiber 17-1shown in FIG. 1A is led via the WDM device 21A to be incident on theoptical fiber amplifier 22, and is amplified thereby. Then, the laserbeam LB3 amplified by the optical fiber amplifier 22 is incident on theoptical fiber amplifier 25 via the WDM device 21B, the narrow bandfilter 24A, the isolator IS3, and WDM device 21C; and the incident laserbeam LB3 is thereby amplified again. Via the WDM device 21D, theamplified laser beam LB3 propagates through one of optical fibers thatconstitute the fiber bundle 19 shown in FIG. 1A (the aforementionedoptical fiber may be an extended portion of an output terminal of theoptical fiber amplifier 25).

The total of amplification gains according to the second-stage opticalfiber amplifiers 22 and 25 is 46 dB (39,810 times) as one example. Whenthe total number of channels (m·n pieces) output from the splitters 16-1to 16-m shown in FIG. 1B is 128, and the average output power of each ofthe channels is about 50 μm, the average output power of all thechannels is about 6.4 mW. When a laser beam of each of the channel isamplified at about 46 dB, the average output power of the laser beamoutput from each of the optical amplifier units 18-1 to 18-n is about 2W. When the above is assumed to have been pulsed at a pulsewidth of 1ns, and a pulse frequency of 100 kHz, the peak output power of each ofthe laser beams is 20 kW. Also, the average output power of the laserbeam Lb6 output from the fiber bundle 19 is about 256 W.

In the present example, coupling losses in the splitters 14 and 16-1 to16-m shown in FIG. 1A are not taken into consideration. However, evenwhen the coupling losses occur, the output powers of the laser beams ofthe individual channels can be unformed to be the above-described value(for example, the peak output power of 20 kW). This can be achieved byincreasing at least one of the amplification gains obtained according tothe optical fiber amplifiers 22 and 25 by the amount of the loss. Inaddition, the value of the output power (output power of the fundamentalwave) of the mono-wavelength oscillatory laser 11 shown in FIG. 1A canbe controlled larger or smaller than the aforementioned value. This canbe achieved by controlling the amplification gains obtained according tothe optical fiber amplifiers 22 and 25.

Referring to the example configuration shown in FIG. 2, the narrow bandfilter 24A removes ASE (amplified spontaneous emission) light occurringin each of the optical fiber amplifier 13 shown in FIG. 1A and theamplifying optical fiber 22 shown in FIG. 2, and lets the laser beam(having a wavelength in width of 1 pm or less) output from themono-wavelength oscillatory laser 11 shown in FIG. 1A to transmit.Thereby, the narrow band filter 24A substantially makes the wavelengthin width of the transmitted beam to be a narrow band. This enables theamplification gain of the laser beam to be prevented from being reducedby the incidence of the ASE light. In this case, the narrow band filter24A preferably has a transmission wavelength in width of about 1 pm.However, since the wavelength in width of the ASE light is several tensof nm, the ASE light can be removed not to cause a problem in practiceeven by using a currently available narrow band filter with atransmission wavelength in width of about 100 pm.

Suppose the output wavelength of the mono-wavelength oscillatory laser11 in FIG. 1A is positively changed. In this case, while the narrow bandfilter 24A may be replaced according to the output wavelength. However,preferably, a narrow band filter having a transmission wavelength inwidth (equivalent to a variable range (about ±20 pm, as mentioned aboveas an example, for an exposure apparatus) is used. Further, the isolatorIS3 reduces the influence of reverse light attributed to nonlineareffects of the optical fibers. Moreover, the ASE noise is reduced.Thereby, the influences of SRS (stimulated raman scattering) and SBS(stimulated brillouin scattering), which are nonlinear effects otherthan those of the last-stage optical fiber amplifier 25, are alsoreduced. Consequently, the wavelength in width expansion is mitigated.The optical amplifier unit 18 may be configured by coupling three ormore stages of optical fiber amplifiers. Also in this case, the narrowband filter 24A and the isolator IS3 are preferably inserted into theboundary portion between the two adjacent optical fiber amplifiers inthe overall configuration.

In the present example, since a large number of the output beams ofoptical amplifier unit 18 are bundled and are used in the bundled state,the intensities of the individual output beams are preferablyhomogenized. This can be implemented in, for example, the followingmanner. A part of the laser beam LB3 output from the WDM device 21D isisolated, the isolated light is photoelectrically converted, and theluminous quantities of laser beams LB3 to be output are therebymonitored. Then, outputs of excitation light sources (semiconductorlasers 23A to 23D) in each of the optical amplifier units 18 arecontrolled so that the aforementioned luminous quantities aresubstantially equal to one another in all the optical amplifier units18.

In the above-described embodiment, the laser light source having anoscillation wavelength of about 1.544 μm is used for the mono-wavelengthoscillatory laser 11. Instead of this laser light source, however, theembodiment may use a laser light source having an oscillation wavelengthin a range of from 1.099 to 1.106 μm. For this laser light source,either a DFB semiconductor laser or an ytterbium(Yb)-doped fiber lasermay be used. In this case, for the optical fiber amplifier in therear-stage optical amplifier section, the configuration may use anytterbium(Yb)-doped fiber amplifier (YDFA) that performs amplificationin a wavelength zone of 990 to 1200 nm including the wavelength of theamplifier section. In this case, ultraviolet light having a wavelengthof 157 to 158 nm wave that is substantially the same wavelength of theF₂ laser can be obtained by outputting the seventh-order harmonic wavein the wavelength conversion section 20 shown in FIG. 1B. In practice,ultraviolet light having substantially the same wavelength as that ofthe F₂ laser can be obtained by controlling the oscillation wavelengthto be about 1.1 μm.

Moreover, the arrangement may be made such that the fourth-orderharmonic wave of the fundamental wave is output in the wavelengthconversion section 20 by controlling the oscillation wavelength in themono-wavelength oscillatory laser 11 to be near 990 nm. This enablesultraviolet light having a same wavelength of 248 nm as that of the KrFexcimer laser to be obtained.

In the last-stage high-peak-output optical fiber amplifier (for example,the optical fiber amplifier 25 shown in FIG. 2), according toabove-described present embodiment, it is preferable to use a large modediameter fiber having a fiber mode diameter of, for example, 20 to 30μm, which is larger than that is ordinarily used (5 to 6 μm), to avoidthe increase in the spectral width according to the nonlinear effects inthe fiber.

Moreover, a double clad fiber having a double clad structure may be usedin place of the large mode diameter fiber to obtain a high level outputin the last-stage optical fiber amplifier (for example, optical fiberamplifier 25 shown in FIG. 2). In this optical fiber, a core portion isdoped with ion that contributes to amplification of laser light, and theamplified laser light propagates through the inside of the core. Anexcitation-dedicated semiconductor laser is coupled to the first cladthat covers the core. The first clad serves in a multimode and has alarge cross section. As such, the high-output excitation-dedicatedsemiconductor laser beam can easily be transmitted therethrough, amultimode-oscillation semiconductor laser can be efficiently coupled,and hence, the excitation-dedicated light source can efficiently beused. A second clad for forming a waveguide of the first clad is formedon the circumference of the first clad.

A quarts fiber or a silicate-based fiber may be used for the opticalfiber amplifier of the above-described embodiment. Alternatively, afluoride-based fiber, such as a ZBLAN fiber, may be used. With thefluoride-based fiber, in comparison to the quartz or silicate-basedfiber, a relatively high erbium dope concentration can be obtained,thereby enabling the fiber length necessary for amplification can bereduced. Particularly, the fluoride-based fiber is preferably used forthe last-stage optical fiber amplifier (optical fiber amplifier 25 shownin FIG. 2). The reduced fiber length enables mitigation in thewavelength-in-width expansion due to the nonlinear effects duringpulse-beam propagation through the fiber. In addition, the reduced fiberlength enables the provision of a narrow-band wavelength in widthnecessary for, for example, the exposure apparatus. The narrow-bandlight source offers an advantage, particularly, when it is used in anexposure apparatus that has a large number of openings. For example, thelight source is advantageous in the design and manufacture of theprojection optical system.

In addition, an optical fiber mainly using phosphate glass oroxidized-bismuth based glass (Bi₂O₃B₂O₃) may be used, particularly forthe last-stage optical fiber amplifier. With the phosphate-glass opticalfiber, the core can be doped at a high concentration with a rare-earthbased element(s) (such as erbium (Er), or both the erbium (Er) andytterbium (Yb)). In this case, in comparison to the conventionalsilicate glass, the fiber length necessary to obtain the same opticalamplification factor is about 1/100 of that with the conventional silicaglass. With the oxidized-bismuth based glass optical fiber, incomparison to the conventional silica glass, the amount of doped erbium(Er) can be increased to be 100 or more times of that with theconventional silica glass. In this case, effects similar to those withthe phosphate glass can be obtained.

In a case where a wavelength of 1.51 to 1.59 μm is used for the outputwavelength of the optical fiber amplifier having the double-structureclads, the fiber core is co-doped with erbium (Er) and ytterbium (Yb)used together as an ion dopant. The co-doping is advantageous to improvethe semiconductor-laser excitation efficiency. That is, when theerbium/ytterbium co-doping is performed, high-ytterbium-absorbingwavelength expands near a region of 915 to 975 nm. By using thewavelength near to aforementioned region, the plurality of semiconductorlasers each having a unique oscillation wavelength are connected throughwavelength division multiplexing (WDM) and coupled to the first clad. Asa result, the plurality of semiconductor lasers can be used asexcitation beams, and a high excitation intensity can therefore beimplemented.

In designing the doped fiber used in the optical fiber amplifier, amaterial is preferably selected to obtain a high gain of the opticalfiber amplifier in a desired wavelength for an apparatus (such as anexposure apparatus) as in the present example that operates at apredetermined wavelength. For example, a material enabling a high gainto be obtained with desired wavelength, for example 1.548 μm, ispreferably selected for an amplifying fiber used in an ultraviolet laserapparatus designed to obtain the same output wavelength (193 to 194 nm)as that of the ArF excimer laser.

However, for wavelength-division-multiplexed communication, acommunication fiber is designed to have a relatively stable gain in awavelength region of several tenth of nm near 1.55 μm. As such, for acommunication fiber including, for example, erbium-monodoped core as anexcitation medium, a method of co-doping a silica fiber with aluminum,phosphorous, and the like is used to implement the stable gain. As such,with the fiber of this type, the gain is not always increased at 1.548μm. Aluminum as a dopant element has the effect of shifting the peaknear 1.55 μm, and phosphorous has the effect of shifting the peak to ashort wavelength side. As such, a small amount of phosphorous can beused as a dopant to increase the gain in a region near 1.547 μm.Similarly, a small amount of phosphorous can be used as a dopant toincrease the gain in a region near 1.547 μm to be even higher when usingthe optical amplifying fiber (such as the double-clad type fiber) havingthe core doped (co-doped) with both erbium and ytterbium.

Hereinbelow, a description will be made regarding example configurationsof the wavelength conversion section 20 used in the ultraviolet lightgenerator of the embodiment shown in FIGS. 1A and 1B.

FIG. 3A shows the wavelength conversion section 20 that is capable ofobtaining the eighth-order harmonic wave through repetition of thesecond-order harmonic wave generation. In FIG. 3A, an output terminal 19a of an optical fiber bundle 19 is, as shown being enlarged, made up ofsuch as 128 optical fibers which are bundled into about 2 mm or smallercircular shape. From the mode portion (core portion) having a diameterof about 20 μm in the each optical fibers, is emitted laser beams eachhaving a wavelength of 1.544 μm (the frequency is represented by “ω”)with a predetermined open angle (numerical aperture), and light bundledwith these laser beams forms a laser beam LB6 as a whole.

The laser beam LB6 (fundamental wave) is incident on a first-stagenonlinear optical crystal 502. The second-order harmonic wave generationis performed therein to generate the second-order harmonic wave having atwofold frequency 2• (wavelength: 1/2 of 772 nm) of the fundamentalwave. The generated second-order harmonic wave is then incident on asecond-stage nonlinear optical crystal 503 through a converging lens505. Similar to the above, through the second-order harmonic wavegeneration, there is generated fourth-order harmonic wave having atwofold frequency of the frequency 2ω0 of the incident wave, that is, afourfold frequency 4ω (wavelength: 1/4 of 386 nm) with respect to thefundamental wave. The generated fourth-order harmonic wave is thentransferred to a third-stage nonlinear optical crystal 504 through aconverging lens 506. Similarly, through the second-order harmonic wavegeneration, there is generated eighth-order harmonic wave having atwofold frequency of the frequency 4ω of the incident wave, that is, aneightfold frequency 8ω (wavelength: 1/8 of 193 nm) with respect to thefundamental wave. The eighth-order harmonic wave is output as laser beamLB5. Thus, the example configuration performs wavelength modulations inthe following order: fundamental wave (wavelength: 1.544μm)→second-order harmonic wave (wavelength: 772 nm)→fourth-orderharmonic wave (wavelength: 386 nm)→eighth-order harmonic wave(wavelength: 193 nm).

Nonlinear optical crystals usable for the above-described wavelengthconversion include, for example, a LiB₃O₅ (LBO) crystal for thenonlinear optical crystal 502 used to convert the fundamental wave intothe second-order harmonic wave, a GdYCOB, that is, aGd_(x)Y_(1−x)Ca₄O(BO₃)₃ crystal (0≦×≦1), for the nonlinear opticalcrystal 503 used to convert the second-order harmonic wave into thefourth-order harmonic wave, and a KAB, that is, a K₂Al₂B₄O₇ crystal forthe nonlinear optical crystal 504 used to convert the fourth-orderharmonic wave into the eight-order harmonic wave.

In this case, the GdYCOB crystal of the present example is made, byadjusting a value of the parameter x which determines a composition, tobe a crystal having an index of double reflection which allowsgenerating a fourth-order harmonic wave from a second-order harmonicwave by a non-critical phase matching (NCPM). The NCPM method does notcause an angular displacement (so-called “walk-off”) between thefundamental wave (second-order harmonic wave) and a harmonic wave(fourth-order harmonic wave) in the nonlinear optical crystal, therebyallowing conversion into the fourth-order harmonic wave with highefficiency. As such, the NCPM method is advantageous in that thegenerated fourth-order harmonic wave is not influenced bywalk-off-caused beam deformation.

Further, since the KAB crystal is used at a portion which generates theeighth-order harmonic wave from the fourth-order harmonic wave, highconversion efficiency can be obtained.

In addition, in the present example, temperature controllers 521, 522and 523 are attached to all nonlinear optical crystals 502, 503 and 504,respectively. The temperature controllers 521 to 523 each include aheating device (such as a heater), a heat sink (such as a Peltierdevice), and a thermal measuring device (such as a thermistor). Thetemperature controllers 521 to 523 control the temperatures of therespective nonlinear optical crystals 502, 503 and 504 to be targettemperatures according to control information received from a controlsection (not shown). According to the temperature control, finalfinetuning of the phase matching angle for wavelength conversion isperformed through the aforementioned NCPM (non-critical phase matching).Walk-off in each of the stages is highly mitigated, and the conversionefficiency is thereby maintained high according to the temperaturecontrol performed to finely tune the phase matching angles of all thenonlinear optical crystals 502 to 504 in the wavelength conversionsection 20.

When the conversion efficiency is allowed to decrease somewhat, thesecond-stage nonlinear optical crystal 503 may be formed of an LBOcrystal. Alternatively, the third-stage nonlinear optical crystal 504may be formed of an SBBO crystal (Sr₂Be₂B₂O₇ crystal).

Referring to FIG. 3A, a converging lens, which is effective forimproving the incidence efficiency of laser beam LB6, is preferablyprovided between the fiber bundle 19 and the nonlinear optical crystal502. In this case, each of the optical fibers constituting the fiberbundle 19 has a mode diameter (core diameter) of about 20 μm, and aregion where the conversion efficiency in the nonlinear optical crystalhas a size of about 200 μm. As such, a lens with a very lowmagnification of about 10× magnification may be provided in units of theoptical fiber to converge the laser beam output from each of the opticalfibers into the nonlinear optical crystal 502. This applies also toother example configurations described below.

FIG. 3B shows a wavelength conversion section 20A that is capable ofobtaining the eighth-order harmonic wave by combining the secondharmonic wave generation and sum frequency generation. Referring to FIG.3B, the laser beam LB6 (fundamental wave) having a wavelength of 1.544μm output from the output terminal 19 a of the fiber bundle 19 isincident on a first-stage nonlinear optical crystal 507 formed of theLBO crystal. In the crystal 507, there is generated the second-orderharmonic wave according to the second harmonic wave generation. Inaddition, a part of the fundamental wave is transmitted as is throughthe nonlinear optical crystal 507. Both the fundamental wave andsecond-order harmonic wave in a linearly polarized state are transmittedtrough a wavelength plate 508 (for example, a 1/2 wavelength plate), andonly the fundamental wave is output in a 90-degree rotated direction ofpolarization. The fundamental wave and the second-order harmonic waveindividually pass through a converging lens 509 and are incident on asecond-stage nonlinear optical crystal 510 formed of the LBO crystal.

In the nonlinear optical crystal 510, there is generated the third-orderharmonic wave from the second-order harmonic wave generated in thenonlinear optical crystal 507 and the fundamental wave transmittedwithout being converted. The above generation is performed according tothe aforementioned sum frequency generation. The third-order harmonicwave generated in the nonlinear optical crystal 510 and the second-orderharmonic wave transmitted without being converted are isolated by adichroic mirror 511. Then, the third-order harmonic wave reflected bythe dichroic mirror 511 is transmitted through a converging lens 513 tobe incident on a third-stage nonlinear optical crystal 514 formed of aGDYCOB crystal. Therein, the third-order harmonic wave is converted bythe second-order harmonic wave generation into the sixth-order harmonicwave (wavelength: 257 nm). A value of the parameter x which determines acomposition of the nonlinear optical crystal 514 is adjusted, so that itgenerates a sixth-order harmonic wave according to non-critical criticalphase matching (NCPM). Thereby, “walk-off” scarcely occurs.

The second-order harmonic wave transmitted through the dichroic mirror511 is incident on a dichroic mirror 516 via a converging lens 512 and amirror M2. In addition, the sixth-order harmonic wave obtained throughthe nonlinear optical crystal 514 is incident on the dichroic mirror 516via a converging lens 515. In this step, the second-order harmonic waveand the sixth-order harmonic wave are coaxially combined, and acomposition thereof is incident on a fourth-stage nonlinear opticalcrystal 517 formed of βP-BaB₂O₄ crystal (BBO crystal). In the nonlinearoptical crystal 517, there is generated the eighth-order harmonic wave(wavelength: 193 nm). The eighth-order harmonic wave is output as anultraviolet laser beam LB5. A CsLiB₆O₁₀ (CLBO) crystal may be used inplace of the BBO crystal for the nonlinear optical crystal 517. Inaddition, when the conversion efficiency is allowed to decreasesomewhat, a BBO crystal may be used for the nonlinear optical crystal514. Thus, the wavelength conversion section 20A performs wavelengthconversion in the following order: fundamental wave (wavelength: 1.544μm)→second-order harmonic wave (wavelength: 772 nm)→third-order harmonicwave (wavelength: 515 nm)→sixth-order harmonic wave (wavelength: 257nm)→eighth-order harmonic wave (wavelength: 193 nm).

Also in the present example, temperature controllers 531 to 534 areattached to all nonlinear optical crystals 507, 510, 514, and 517,respectively, to control the temperatures of the respective nonlinearoptical crystals; and the phase matching angles are individually finelytuned through the temperature control. In this case, the temperatures ofthe nonlinear optical crystals 507 and 510 are set to be different fromeach other.

As described above, the present example has the configuration in whichone of the sixth-order harmonic wave and second-order harmonic wavepasses through a split optical path and is then incident on thefourth-stage nonlinear optical crystal 517. In the configuration, theconverging lenses 515 and 512 individually converging the sixth-orderharmonic wave and the second-order harmonic wave into the fourth-stagenonlinear optical crystal 517 can be disposed on optical paths differentfrom each other. In this case, even if “walk-off” narrowly occurs in thethird-stage nonlinear optical crystal 514, and the output sixth-orderharmonic wave has an elliptical cross section, as in the presentexample, by disposing the individual converging lenses 515 and 512 ondifferent optical paths, for example, a cylindrical lens pair can beused for the converging lens 515, thereby enabling the beam-shaping forthe sixth-order harmonic wave to easily be implemented. Hence, theconversion efficiency can be improved by increasing overlapping portionswith the second-order harmonic wave in the fourth-stage nonlinearoptical crystal 517.

The configuration between the second-stage nonlinear optical crystal 510and the fourth-stage nonlinear optical crystal 517 is not limited tothat shown in FIG. 3B. This configuration may be arbitrarily arranged aslong as it has the same optical path lengths for the sixth-orderharmonic wave and the second harmonic wave to cause the sixth-orderharmonic wave and the second harmonic wave to be incident on thefourth-stage nonlinear optical crystal 517. Moreover, for example, thethird-stage and fourth-stage nonlinear optical crystals 514 and 517 maybe disposed on the same optical axis of the second-stage nonlinearoptical crystal 510. In this configuration, the third-stage nonlinearoptical crystal 514 is used to convert only the third-order harmonicwave into the sixth-order harmonic wave according to the second-orderharmonic wave generation, and the converted harmonic wave and thenon-converted second-order harmonic wave together may be incident on thefourth-stage nonlinear optical crystal 517. This configuration avoidsthe necessity of using the dichroic mirrors 511 and 516.

Next, FIG. 4 shows another wavelength conversion section 20B thatenables the eighth-order harmonic wave to be generated throughcombination of the second harmonic wave generation and the sum frequencygeneration. Referring to FIG. 4, the laser beam LB6 (fundamental wave),having a wavelength of 1.544 μm, which has been output from the outputterminal 19 a of the fiber bundle 19, is incident on a first-stagenonlinear optical crystal (LBO crystal) 601, in which a second-orderharmonic wave is generated according to the second-order harmonic wavegeneration. In addition, a part of the fundamental wave is transmittedas it is therethrough. In this case, an image of the output terminal 19a (images of a large number of thin luminous fluxes) is formed near acenter of the nonlinear optical crystal 601 by a converging lens (notshown). The images of the large number of the luminous fluxes arerelayed successively into the succeeding nonlinear optical crystal.

Both the fundamental wave and second-order harmonic wave transmit in alinearly polarized state through a wavelength plate 602 (such as a 1/2wavelength plate), and only the fundamental wave is output with itsdirection polarization being rotated 90-degree. The fundamental wave andthe second-order harmonic wave individually pass through a converginglens 603, and are incident on a second-stage nonlinear optical crystal(LBO crystal) 604.

In the nonlinear optical crystal 604, a third-order harmonic wave isobtained from an incident second-order harmonic wave and a fundamentalwave, and a part of the fundamental wave and a part of the second-orderharmonic wave are transmitted without being converted in wavelength. Thethird-order harmonic wave, which has been obtained through thesecond-stage nonlinear optical crystal 604, and the second-orderharmonic wave, which has transmitted without wavelength conversion, areisolated by a dichroic mirror 605. The third-order harmonic wavereflected by the dichroic mirror 605 forms an image of an outputterminal 19 a (image of a large number of luminous fluxes) through ananisotropic converging lens 610, formed of two cylindrical lens, and amirror 611. A cylindrical-lens array 612 is disposed near a formed planeof the aforementioned image to convert the image of the individualluminous fluxes at an image having magnifications that are different intwo directions perpendicular to each other. The third-order harmonicwave transmitted through the cylindrical-lens array 612 passes throughan isotropic converging lens 613 and is then incident on a dichroicmirror 614.

On the other hand, the fundamental wave and the second-order harmonicwave, which have transmitted through the dichroic mirror 605, passesthrough a converging lens 606 and is then incident on a third nonlinearoptical crystal 607 (LBO crystal). Through the third nonlinear opticalcrystal 607, the second-order harmonic wave is converted into afourth-order harmonic wave according to second-order harmonicgeneration. Then, the fourth-order harmonic wave and the fundamentalwave transmitted without being converted are isolated by a dichroicmirror 608 from each other. Specifically, the fourth-order harmonic wavereflected by the dichroic mirror 608 is incident on the dichroic mirror614 through an anisotropic converging lens 609 formed of two cylindricallenses. Then, the third-order harmonic wave and the fourth-orderharmonic wave that have coaxially been combined through a dichroicmirror 614 are incident on a fourth-stage nonlinear optical crystal 615formed of a β-BaB₂O₄ crystal (BBO crystal). Thereby, a seventh-orderharmonic wave is obtained therefrom according to sum frequencygeneration. The seventh-order harmonic wave is then incident on adichroic mirror 617 through a converging lens 616.

The fundamental wave transmitted through the dichroic mirror 608 thenforms an image of the output terminal 19 a (image of a large number ofthe luminous fluxes) through an anisotropic converging lens 618 formedof two cylindrical lens. A cylindrical-lens array 619 is disposed near aformed plane of the aforementioned image to convert the image of theindividual luminous fluxes at an image having magnifications that aredifferent in two directions perpendicular to each other. The fundamentalwave transmitted through the cylindrical-lens array 619 then transmitsthrough a mirror 620 and an isotropic converging lens 621, and is thenincident on the dichroic mirror 617. The seventh-order harmonic wave andthe fundamental wave that have coaxially been combined through thedichroic mirror 617 are incident on a fifth-stage nonlinear opticalcrystal 622 formed of an LB4 crystal, namely, an Li₂B₄O₇ (lithiumtetraborate) crystal. Therein, an eighth-order harmonic wave(wavelength: 193 nm) is obtained according to sum frequency generation.The eighth-order harmonic wave is then output as a laser beam LB5 in theform of ultraviolet light. For the fifth-stage nonlinear optical crystal622, a KAB crystal (K₂Al₂B₄O₇ crystal) may be used to replace the LB4crystal. The wavelength conversion section 20B performs wavelengthconversion in the order: fundamental wave (wavelength: 1.544 μm)second-order harmonic wave (wavelength: 772 nm)→third-order harmonicwave (wavelength: 515 nm)→fourth-order harmonic wave (wavelength: 386nm)→seventh-order harmonic wave (wavelength: 221 nm)→eighth-orderharmonic wave (wavelength: 193 nm).

In the present example, the fourth-order harmonic wave, generatedthrough the nonlinear optical crystal 607 according to the secondharmonic generation, and the seventh-order harmonic wave, generatedthrough the nonlinear optical crystal 615 according to the sum frequencygeneration, are each deformed to be ellipse (anisotropic) in across-sectional view because of the walk-off phenomenon. However, alaser beam LB6 to be incident in the present example is an aggregate ofa large number of thin luminous fluxes (128 fluxes in the presentexample) each having a predetermined opening, the cross-sectional shapesof the large number of luminous fluxes forming the fourth-order harmonicwave and the seventh-order harmonic wave are discretely deformed to beanisotropic. As such, a fourth-order harmonic wave 660 generated by thenonlinear optical crystal 607 and a third-order harmonic wave 650generated by the nonlinear optical crystal 604 that are shown in FIG. 4individually have cross-sectional shapes as shown in FIG. 5.Specifically, the fourth-order harmonic wave 660 is an aggregate ofluminous fluxes 660 a each having an elliptical cross-sectional shape,and the third-order harmonic wave 650 is an aggregate of luminous fluxes650 a each having a circular cross-sectional shape. Consequently, whenthe third-order harmonic wave 650 and the fourth-order harmonic wave 660are simply overlapped to form a composite wave 670, the ratio of anoverlapped portion in each luminous flux 670 a forming the compositewave 670 is so small as to cause the conversion efficiency to decrease.

To increase the ratio of the overlapped portion in the composite wave,the present example is arranged such that the fourth-order harmonic wave660 shown in FIG. 4 is first longitudinally reduced and is therebyconverted into a fourth-order harmonic wave 661 formed of luminousfluxes 661 a each having a substantially circular cross-sectional shapeas shown in FIG. 6. In the figures, the fourth-order harmonic wave 660represents the shape in a state of having been imaged through thenonlinear optical crystal 607. The fourth-order harmonic wave 661represents the shape in a state of having been imaged through thenonlinear optical crystal 615. Concurrently, the third-order harmonicwave 650 shown in FIG. 4 is reduced through the anisotropic converginglens 610 in the same direction as that for the fourth-order harmonicwave 660 to thereby obtain a uniformed overall cross-sectional shape.Consequently, as shown in FIG. 6, while a third-order harmonic wave 651thus obtained has the same overall cross-sectional shape as that of thefourth-order harmonic wave 661, the shape of each luminous flux 651 a isformed elliptical, and the ratio of a portion overlapping with theluminous flux 661 a is reduced. In the figures, the third-order harmonicwave 650 represents the shape in a state of having been imaged throughthe nonlinear optical crystal 604. The third-order harmonic wave 651represents the shape in a state of having been imaged through theanisotropic converging lens 610.

In the state illustrated in FIG. 4, to increase the ratio of theoverlapped portion, the cylindrical-lens array 612 is used to convertthe cross-sectional shape of each of the luminous fluxes tosubstantially be circular. A third-order harmonic wave 652 thusobtained, as shown in FIG. 6, is uniformed in overall cross-sectionalshape with the fourth-order harmonic wave 661. In addition, each of theluminous flux 651 a is uniformed in cross-sectional shape with theluminous flux 661 a of the fourth-order harmonic wave 661. In addition,since the converging lens 613 is isotropic, the third-order harmonicwave 652 is relayed to the nonlinear optical crystal 615 at the sameaspect ratio at the incident time. As a result, the seventh-orderharmonic wave is generated at the highest conversion efficiency in thenonlinear optical crystal 615.

In addition, also a large number of luminous fluxes forming theseventh-order harmonic wave generated by the nonlinear optical crystal615 are formed elliptical. As such, in the last stage of nonlinearoptical crystal 622, to uniform the overall cross-sectional shapes ofthe seventh-order harmonic wave and the fundamental wave and to uniformcross-sectional shapes of the individual luminous fluxes, thefundamental wave transmitted through the nonlinear optical crystal 607is once imaged through the anisotropic converging lens 618. Thereafter,an image of each of the luminous fluxes is deformed through thecylindrical-lens array 619. Thereby, the eighth-order harmonic wave isgenerated by the nonlinear optical crystal 622 at the highest conversionefficiency.

Moreover, referring to FIG. 4, the cylindrical-lens arrays 612 and 619are respectively disposed on the optical path of the third-orderharmonic wave (wavelength: 515 nm) and the optical path of thefundamental wave (wavelength: 1.544 μm). Many types of materials fortransmitting the substantially visible and infrared light are available.As such, the manufacture of the cylindrical-lens arrays 612 and 619 isfacilitated.

In the above-described embodiment, the cylindrical-lens arrays 612 and619 are each used as an anisotropic optical system having differentmagnifications in the crossing two directions. However, the embodimentmay instead use one of a microlens array and a diffractive opticalelement (DOE). In this case, the microlens array is formed of the samenumber of anisotropic lens as that of the luminous fluxes which formsthe incident laser beam. Concurrently, the diffractive optical elementis formed of an aggregate of the same number of fine diffractiongratings as that of the aforementioned luminous fluxes.

For each of the wavelength conversion sections 20 and 20A shown in FIGS.3A and 3B, per-channel average output power of the eighth-order harmonicwave (wavelength: 193 nm) was estimated. From the result, it wasverified that when the per-channel incident laser beam is characterizedby a peak power of 20 kW, a pulsewidth of 1 ns, a pulse repetitionfrequency of 100 kHz, and an average output power of 2W, any one of thewavelength conversion sections 20, 20A, and 20B was verified to becapable of providing ultraviolet light having a wavelength of 193 nm,which is sufficient output as an exposure apparatus-dedicated exposurelight source, in the overall configuration including 128 channels.

A configuration similar to the wavelength conversion section 20, 20A,20B can be arranged to perform the wavelength conversion in thefollowing order: fundamental wave (wavelength: 1.544 μm)→second-orderharmonic wave (wavelength: 772 nm)→fourth-order harmonic wave(wavelength: 386 nm)→sixth-order harmonic wave (wavelength: 257nm)→eighth-order harmonic wave (wavelength: 193 nm). Furthermore, theeighth-order harmonic wave can be obtained through the wavelengthconversion performed in the following order: fundamental wave(wavelength: 1.544 μm)→second-order harmonic wave (wavelength: 772nm)→third-order harmonic wave (wavelength: 515 nm)→fourth-order harmonicwave (wavelength: 386 nm)→sixth-order harmonic wave (wavelength: 257nm)→seventh-order harmonic wave (wavelength: 221 nm)→eighth-orderharmonic wave (wavelength: 193 nm). It is preferable to select one ofthe above configurations that has a relatively high conversionefficiency and that can be simplified.

To have ultraviolet light having substantially the same wavelength asthat of the F₂ laser (wavelength: 157 nm), as the wavelength conversionsection 20, the configuration may be arranged to use a wavelengthconversion section capable of generating the tenth-order harmonic wavewith 1.57 μm wavelength of the fundamental wave generated in themono-wavelength oscillatory laser 11 shown in FIG. 1A. To implement theabove, for example, the wavelength conversion may be performed in thefollowing order: fundamental wave (wavelength: 1.57 μm)→second-orderharmonic wave (wavelength: 785 nm)→fourth-order harmonic wave(wavelength: 392.5 nm)→eighth-order harmonic wave (wavelength: 196.25nm)→tenth-order harmonic wave (wavelength: 157 nm).

In addition, a different method may be employed to obtain ultravioletlight having substantially the same wavelength as the wavelength (157nm) of the F₂ laser. A method can be envisaged that uses a wavelengthconversion section as the wavelength conversion section 20, which iscapable of generating the seventh-order harmonic wave with the 1.099-μmwavelength of the fundamental wave generated in the mono-wavelengthoscillatory laser 11. In this case, for example, the wavelengthconversion may preferably be performed in the following order:fundamental wave (wavelength: 1.099 μm)→second-order harmonic wave(wavelength: 549.5 nm)→third-order harmonic wave (wavelength: 366.3nm)→fourth-order harmonic wave (wavelength: 274.8 nm)→seventh-orderharmonic wave (wavelength: 157 nm). Also in these cases, high conversionefficiency can be obtained by appropriately employing a configurationsimilar to that of the embodiment shown in FIGS. 3A and 3B or FIG. 4.

FIG. 8 shows another example configuration of the wavelength conversionsection 20. Referring to FIG. 8, a laser beam LB6 (fundamental wave)having a wavelength of 1.544 μm is incident on a nonlinear opticalcrystal 702 (LBO crystal) via a lens 701, a second-order harmonic waveof the fundamental wave is generated therethrough, and also a part ofthe fundamental wave transmits therethrough. The fundamental wave andthe second-order harmonic wave are isolated by a dichroic mirror 703from each other. The fundamental wave is incident on a dichroic mirror708 through a mirror 706 and a lens 707, and the second-order harmonicwave is incident on the dichroic mirror 708 through a mirror 705. Thelight combined through the dichroic mirror 708 generates a third-orderharmonic wave in a nonlinear optical crystal 709 (LBO crystal). Thefundamental wave, the second-order harmonic wave, and the third-orderharmonic wave also pass through the nonlinear optical crystal 709.

The fundamental wave is led to a dichroic mirror 721 through thedichroic mirrors 710 and 711 and a mirror 712. The second-order harmonicwave is led to pass through a lens 716 and is then converted into afourth-order harmonic wave through a nonlinear optical crystal 717(formed of, for example, one of the LBO, CLBO, BBO, and LB4 or thelike). Thereafter, the converted fourth-order harmonic wave is incidenton a nonlinear optical crystal 719 (BBO crystal) through a lens 718 anda dichroic mirror 715. The third-order harmonic wave is incident on anonlinear optical crystal 719 through a lens 713, a mirror 714, and thedichroic mirror 715. Therethrough, a seventh-order harmonic wave isgenerated from the third-order harmonic wave and the fourth-orderharmonic wave according to the sum frequency generation. Theseventh-order harmonic wave is led to the dichroic mirror 721 through alens 722. The fundamental wave and the seventh-order harmonic wavecombined through the dichroic mirror 721 are converted into aneighth-order harmonic wave (wavelength: 193 nm) through a nonlinearoptical crystal 723 (formed of, for example, LBO, BBO, CLBO, or KAB).The eighth-order harmonic wave is output as a laser beam LB5 in the formof ultraviolet light. The wavelength conversion section performswavelength conversion in the following order: fundamental wave(wavelength: 1.544 μm)→second-order harmonic wave→third-order harmonicwave→fourth-order harmonic wave→seventh-order harmonic wave→eighth-orderharmonic wave (wavelength: 193 nm).

In the present example, in each of, for example, the lenses 701, 704,707, and 713 are used to pass the mono-wavelength light. Hence, nochromatic aberrations occur with the lenses, and the conversionefficiency can thereby be improved.

FIG. 9A shows another example configuration of the wavelength conversionsection 20. Referring to FIG. 9A, a laser beam LB6 (fundamental wave)having a wavelength of 1.544 μm is incident on a nonlinear opticalcrystal 802 (LBO crystal) via a lens 801, a second-order harmonic waveis generated therethrough, and also a part of the fundamental wavetransmits therethrough. The fundamental wave and the second-orderharmonic wave are isolated by a dichroic mirror 803 from each other. Thefundamental wave is incident on a dichroic mirror 808 through a mirror806 and a lens 807, and the second-order harmonic wave is incident onthe dichroic mirror 808 through a mirror 805. The light combined throughthe dichroic mirror 808 generates a third-order harmonic wave in anonlinear optical crystal 809 (LBO crystal); and the fundamental wave,the second-order harmonic wave, and the third-order harmonic wave passesthrough the nonlinear optical crystal 809.

The fundamental wave is led to a dichroic mirror 816 through thedichroic mirrors 810, 813 and a mirror 814. The second-order harmonicwave is led to pass through the dichroic mirror 810, a lens 811, amirror 812, and a dichroic mirror 818 and is then incident on anonlinear optical crystal 819 (formed of, for example, one of LBO, CLBO,BBO, and LB4). The third-order harmonic wave passes through the dichroicmirrors 810 and 813, a lens 817, and the dichroic mirror 818, and isthen incident on the nonlinear optical crystal 819. A fifth-orderharmonic wave is generated in the nonlinear optical crystal 819, and apart of the second-order harmonic wave is transmitted therethroughwithout being converted. Then, the second-order harmonic wave isincident on a nonlinear optical crystal 826 (formed of one of CLBO andBBO) through a dichroic mirror 820, a lens 821, a mirror 822, and adichroic mirror 825. The fifth-order harmonic is incident on a nonlinearoptical crystal 826 through the dichroic mirror 820, a mirror 823, alens 824, and the dichroic mirror 825. Therethrough, a seventh-orderharmonic wave is generated from the second-order harmonic wave and thefifth-order harmonic wave according to the sum frequency generation. Theseventh-order harmonic wave is led to the dichroic mirror 816 through amirror 827 and a lens 828. The fundamental wave and the seventh-orderharmonic wave combined through the dichroic mirror 816 are convertedinto an eighth-order harmonic wave (wavelength: 193 nm) through anonlinear optical crystal 829 (formed of, for example, LBO, CLBO, or KABor the like). The eighth-order harmonic wave is output as a laser beamLB5 in the form of ultraviolet light. The wavelength conversion sectionperforms wavelength conversion in the following order: fundamental wave(wavelength: 1.544 μm)→second-order harmonic wave→third-order harmonicwave→fifth-order harmonic→wave seventh-order harmonic wave→eighth-orderharmonic wave (wavelength: 193 nm).

As a result, since the seventh-order harmonic wave need not be generatedaccording to the sum frequency generation, BBO having absorption withthe seventh-order harmonic wave (wavelength: 221 nm) need not be used.Hence, the durability is improved, and in addition, the phase-matchingtolerance is increased. With a sixth-order harmonic wave (258 nm) or afifth-order harmonic wave (309 nm), the absorption by BBO issufficiently less in comparison to the seventh-order harmonic wave. Assuch, even with BBO being used, a high durability can be obtained. Inaddition, since the absorption of a fifth-order harmonic wave by BBO isless than that of a sixth-order harmonic wave, the BBO is preferablyused for generating the fifth-order harmonic wave. In addition, theeighth-order harmonic wave (193 nm) can be generated without the BBO.

Also in an example shown in FIG. 9A, for example, the individual lenses801, 804, 807, and 817 or the like are used to pass through themono-wavelength light, no chromatic aberrations occur with the lenses.Hence, the conversion efficiency can be improved.

An example configuration shown in FIG. 9B performs wavelength conversionin the following order: fundamental wave (wavelength: 1.544μm)→second-order harmonic wave→third-order harmonic wave→sixth-orderharmonic wave→seventh-order harmonic wave→eighth-order harmonic wave(wavelength: 193 nm). A nonlinear optical crystal 832 for thesecond-order harmonic wave generation (ω+ω→2ω) is formed of LBO; anonlinear optical crystal 839 for the third-order harmonic wavegeneration (ω+2→3ω) is formed of LBO; a nonlinear optical crystal 841for the sixth-order harmonic wave generation (3ω+3ω→6ω) is formed of oneof BBO, LB4, and CLBO; a nonlinear optical crystal 847 for theseventh-order harmonic wave generation (ω+6ω→7ω) is formed of one of LBOand LB4 (BBO is also usable); and a nonlinear optical crystal 854 forthe eighth-order harmonic wave generation (ω+7ω→8ω) is formed of one of,for example, LBO, CLBO, and KAB. In addition, in the configuration,there are disposed lenses 831, 836, 837, 842, 845, 852, and 850; mirrors834, 835, 843, 844, 851, and 849; and dichroic mirrors 833, 838, 840,846, 848, and 853.

Similarly, an example configuration shown in FIG. 10A performswavelength conversion in the following order: fundamental wave(wavelength: 1.544 μm)→second-order harmonic wave→fourth-order harmonicwave→fifth-order harmonic wave→seventh-order harmonic wave→eighth-orderharmonic wave (wavelength: 193 nm). A nonlinear optical crystal 902 forthe second-order harmonic wave generation (ω+ω→2ω) is formed of LBO; anonlinear optical crystal 906 for the fourth-order harmonic wavegeneration (2ω+2ω=4ω) is formed of one of LBO and YCOB; a nonlinearoptical crystal 912 for the fifth-order harmonic wave generation(ω+4ω→5ω) is formed of one of LBO, CLBO, BBO and LB4; a nonlinearoptical crystal 921 for the seventh-order harmonic wave generation(2ω+5ω→7ω) is formed of CLBO (BBO is also usable); and a nonlinearoptical crystal 920 for the eighth-order harmonic wave generation(ω+7ω→8ω) is formed of one of, for example, LBO, CLBO, and KAB or thelike. In addition, in the configuration, there are disposed lenses 901,905, 907, 910, 913, 915, 923, and 918; mirrors 904, 909, and 917; anddichroic mirrors 903, 908, 911, 914, 916, and 919.

Similarly, an example configuration shown in FIG. 10B performswavelength conversion in the following order: fundamental wave(wavelength: 1.544 ρm)→second-order harmonic wave→fourth-order harmonicwave→sixth-order harmonic wave→seventh-order harmonic wave→eighth-orderharmonic wave (wavelength: 193 nm). A nonlinear optical crystal 932 forthe second-order harmonic wave generation (ω+ω→2ω) is formed of LBO; anonlinear optical crystal 935 for the fourth-order harmonic wavegeneration (2ω+2ω4ω) is formed of one of LBO and YCOB; a nonlinearoptical crystal 942 for the sixth-order harmonic wave generation(2ω+4ω→6ω) is formed of one of CLBO, BBO and LB4; a nonlinear opticalcrystal 921 for the seventh-order harmonic wave generation (ω+6ω→7ω) isformed of one of CBO and LB4 (BBO is also usable); and a nonlinearoptical crystal 954 for the eighth-order harmonic wave generation(ω+7ω→8ω) is formed of one of, for example, LBO, CLBO, and KAB or thelike. In addition, in the configuration, there are disposed lenses 931,934, 938, 940, 943, 946, 952, and 949; mirrors 945, 937, 939, 951, and950; and dichroic mirrors 936, 941, 944, 948, and 950.

In either of the example configurations shown in FIGS. 9A, 9B, 10A and10B, no lens chromatic aberration occurs. Moreover, the seventh-orderharmonic wave is generated without third-order and fourth-order harmonicwaves.

As is apparent from FIG. 1A, in the above-described embodiment, thecombined light of the outputs of the n optical amplifier units 18-1 to18-n in the m-group is converted in wavelength by using the singlewavelength conversion section 20 to 20B. Alternatively, however, theconfiguration may be arranged such that, for example, m′ units (m′=“2”or larger inger) wavelength conversion sections are provided. In thealternative configuration, the outputs of the m-group optical amplifierunits 18-1 to 18-n are divided in units of n′ outputs into m′ groups,the wavelength conversion is performed for one of the wavelengthconversion section in units of one of the groups, and the obtained m′ultraviolet light beams (in the present example, m′=“4”, “5”, or thelike) are combined. Thus, the wavelength conversion section 20 is notlimited to that having the above-described configuration. Moreover, forexample, a CBO crystal (CsB₃O₅), may be used as an alternative crystalfor the nonlinear optical crystal.

According to the ultraviolet light generator of the above-describedembodiment, the diameter of the output terminal of the fiber bundle 19,shown in FIG. 1A, even with all the channels being included, is about 2mm or smaller. As such, one or several units of the wavelengthconversion sections 20 are sufficient to perform the wavelengthconversion of all the channels. In addition, since flexible opticalfibers are used for the output terminals, the flexibility inconfiguration is very high. For example, the configuration sections suchas the wavelength conversion section, the mono-wavelength oscillatorylaser, and the splitter, can be separately disposed. Consequently, theultraviolet light generator of the present example enables the provisionof an ultraviolet laser device that is inexpensive and compact, and hasa low spatial coherence while it is of a mono-wavelength type.

Hereinbelow, an example exposure apparatus using the ultraviolet lightgenerator shown in FIG. 1A will be described.

FIG. 7 shows an exposure apparatus of the present example. Referring toFIG. 7, component members provided between the mono-wavelengthoscillatory laser 11 and the m-group optical amplifier units 18-1 to18-n in the ultraviolet light generator shown in FIG. 1A are used for anexposure light source 171. The ultraviolet light generator is tuned tobe capable of converting the laser beam LB5 finally output into light inan ultraviolet region with one of wavelengths of 193 nm, 157 nm, andothers.

Most of a laser beam (fundamental wave) output from a light-sourcemainbody section 171 is fed to an illumination system 162 via acoupling-dedicated optical fiber 173 and a wavelength conversion section172. The rest of the laser beam is fed to an alignment system (describedbelow in detail) via a coupling-dedicated optical fiber 178. Thecoupling-dedicated optical fibers 173 and 178 individually correspond tobeams obtained by splitting the light in a fiber bundle 19 shown in FIG.1A.

The wavelength conversion section 172 (which corresponds to thewavelength conversion section 20 shown in FIG. 1A) converts thewavelength of the fundamental wave received from a light-source mainbodysection 171, and outputs ultraviolet-region exposure light formed of thelaser beam LBS. The illumination system 162 is configured of, forexample, an optical integrator (homogenizer) for homogenizingilluminance distributions of the exposure light, an aperture diaphragm,a field diaphragm (reticle blind), and a condenser lens. In theaforementioned configuration, the exposure light output from theillumination system 162 illuminates a slit-like illumination region of apattern surface of a reticle 163 set as a mask to provide a homogeneousilluminance distribution. In the present example, since the spatialcoherence of the exposure light is so low that the configuration of amember for reducing the spatial coherence in the illumination system 162can be simplified, and the exposure apparatus can therefore be furtherminiaturized.

The reticle 163 is set on a reticle stage 164. The exposure lighttransmitted through the reticle 163 is used to project a demagnifiedimage of a pattern in the illumination region onto a wafer 166(exposure-target substrate) via a projection optical system 165. Theprojection is performed at a magnification M_(RW) (for example, 1/4,1/5, 1/6, or the like). For the projection optical system 165, any oneof a dioptric system, a reflection system, or a catadioptric system isusable. However, when using vacuum ultraviolet light for the exposurelight, since materials having high transmittance is limited, thecatadioptric system may preferably used to improve the imagingperformance. The wafer 166 is coated with photoresist, and is adisc-like substrate, such as a semiconductor (silicon or the like) or aSOI (silicon on insulator).

The wafer 166 is held on a wafer stage 167, and the three-dimensionalposition of the wafer 166 is defined by the wafer stage 167 driven by adrive section 169. In addition, the reticle stage 164 is driven by adriving mechanism 168 to be two-dimensionally movable and rotatable. Thedriving section 169 and the driving mechanism 168 are controlled by aprimary control system 177. At the time of exposure, under the controlof the primary control system 177, the wafer 166 is positioned throughstepping movements of the wafer stage 167. Thereafter, the reticle 163is scanned via the reticle stage 164 in a predetermined direction withrespect to the illumination region, and the image of the pattern of thereticle 163 is transferred on each shot region of the wafer 166according to step-and-scan method. In this case, the step-and-scanmethod performs scanning the wafer 166 via the wafer stage 167 by usingthe magnification M_(RW) as a velocity ratio. Thus, the exposureapparatus of the present example is of a scan-exposure type. However, itshould be apparent that the exposure light source 171 can be appliedalso to an exposure apparatus, such as a stepper, of afull-field-exposure type.

In the above-described case, since the exposure light source 171 and thewavelength conversion section 172 (light-source system) of the presentexample are small, it may be immobilized together with at least aportion (such as the wavelength conversion section 172) of thelight-source system on a frame provided for supporting the illuminationsystem 162. Alternatively, the exposure light source 171 may beindependently disposed. However, a powersupply and the like to becoupled to the exposure light source 161 are preferably disposedseparately.

As described above, the exposure apparatus using the ultraviolet lightgenerator of the present example is smaller in comparison with theconventional one using another type (exposure apparatus using, forexample, the excimer laser or the arrayed laser). In addition, since theexposure apparatus is configured of elements coupled using the opticalfibers, the exposure apparatus has a high flexibility in disposition ofthe individual units used for the configuration thereof.

Exposure-light-amount control in the above-described scan-exposureoperation may be implemented in the following manner. Control isperformed for at least one of the pulse repetition frequency f, which isdefined by the optical modulating device 12 shown in FIG. 1A, and theinterchannel delay time, which is defined by the delaying devices(optical fibers 15-1 to 15-m, and 17-1 to 17-n). The control is thusperformed to cause the exposure light source 171 to oscillate aplurality of pulse beams at equal time intervals during scan-exposureoperation. In addition, according to the sensitivity property of thephotoresist, at least one of the optical intensity of the pulse beam onthe wafer 166, the scan speed for the wafer 166, the pulse-beamoscillation interval (frequency), and the width of the pulse beam in thescan direction for the wafer 166 (that is, an radiation region thereof)to thereby control the integrated luminous quantity of a plurality ofpulse beams irradiated in a period in which the individual points of thewafer traverse the radiation region. At this time, in consideration ofthe throughput, least one of other control parameters representing thepulse-beam optical intensity, the oscillation frequency, and theradiation region width is preferably controlled so that the scan speedfor the wafer 166 is substantially maintained to be the maximum speed ofthe wafer stage 167.

In addition, in the present example, since the coupling-dedicatedoptical fiber 173 and a coupling-dedicated optical fiber 178 are used,the light-source mainbody section 171 can be provided outside of theexposure apparatus mainbody. The configuration built as described aboveenables major configuration portions involving heat generation to bedisposed outside of the exposure apparatus mainbody. The majorconfiguration portions include an excitation-dedicated semiconductorlaser for the optical fiber amplifier, a driving powersupply for thesemiconductor laser, and a temperature controller. As such, theconfiguration enables the mitigation or avoidance of heat-attributedproblems, such as a problem of optical-axis misalignment that can occurwhen the exposure apparatus mainbody is influenced by heat generated inthe ultraviolet light generator provided as the exposure light source.

In addition, the reticle stage 164 of the present example is configuredso that it is driven by the driving mechanism 168 to be movable in the Xand Y directions and to be finely rotatable. Further, a reference markplate FM is provided on the wafer stage 167. The reference mark plate FMis used for, for example, baseline measurement described below.Moreover, the present example includes an alignment system 180 providedfor detecting an alignment mark on the reticle 163, and an alignmentsystem 181 of an off-access method that operates without the projectionoptical system 165.

In the present example, a laser beam (fundamental wave) from thelight-source mainbody section 171 is fed to a wavelength conversionsection 179 for the alignment system 180 via an optical fiber 178. Forthe wavelength conversion section 179, the present example uses awavelength conversion section that is similar to the wavelengthconversion section 20 shown in FIG. 1A and that is relatively small. Thewavelength conversion section 179 is integrally provided on the framethat holds the alignment system 180, in which laser beam LB5 having thesame wavelength as that of the exposure light that has been output fromthe wavelength conversion section 179 is used as illumination light AL.

The above-described arrangement avoids the necessity of providing anlight source for the alignment system 180. In addition, the referencemark or the alignment mark can be detected by using illumination lighthaving the same wavelength as that of exposure light, and accurate markdetection can be implemented. That is, the alignment system 180 radiatesillumination light AL having the same wavelength of exposure light ontothe alignment mark and onto a reference mark on the reference mark plateFM through the projection optical system 165. In addition, the alignmentsystem 180 uses an image-capturing device (CCD) to receive lightgenerated from the aforementioned two marks, and is used for, forexample, alignment of the reticle 163 and baseline measurement of thealignment system 181.

The off-access alignment system 181 radiates white light (broad bandlight) having a wavelength in width of about 550 to 750 nm onto thealignment mark on the wafer 166. In addition, the alignment system 181causes an image of an index mark and an image of the alignment mark tobe imaged on the image-capturing device (CCD), and detects positionaldisplacements of the two marks.

In this case, when the alignment systems 180 and 181 are used toindividually detect the reference mark on the reference mark plate FM,the amount of the baseline (gap between the detection center and theexposure center) can be measured from the detection results. Alignmentof each shot region of the wafer 166 is implemented at high accuracyaccording to this result and the measurement result of the alignmentsystem 181. The baseline measurement is performed prior to the start ofexposure of the wafer. However, the baseline measurement may beperformed each time the wafer is replaced; or alternatively, themeasurement may be performed at a ratio of about one time with respectto the exposure operation for a plurality of wafers. However, thebaseline is inevitably measured after the reticle has been replaced.

The optical fiber (including the optical fiber amplifier and the like)used in the above-described embodiment may preferably be covered with alow-degassing material, such as Teflon or fluorine-based resin. Foreignmatters (including fibrous matters and the like) occurred from theoptical fiber can be contaminants that contaminates, and the opticalfiber is covered as described above to prevent the occurrence of thecontaminants. However, instead of covering the optical fiber with theTeflon or the like, the optical fibers disposed in chambers may becollectively stored in a stainless steel housing.

The exposure apparatus of the above-described embodiment shown, forexample, in FIG. 7, may include a spatial-image measuring system. Thespatial-image measuring system may be such that the mark provided on thereticle 163 and the reference mark provided on the reticle stage 164 areilluminated with illumination light having the same wavelength, and amark image formed by the projection optical system 165 is detectedthrough an opening (such as a slit) provided on the wafer stage 167. Inthis case, for a light source generating the illumination light for thespatial-image measuring system, a light source having the sameconfiguration as that of the above-described light source (171 and 179)may be separately provided. Alternatively, the exposure-dedicated lightsource formed of the members including the exposure light source 171 andthe illumination system 162 may be shared.

The exposure apparatus of the above-mentioned embodiment can bemanufactured in the following manner. The illumination optical systemand the projection optical system, which are formed to include theplurality of lenses, are built into the exposure apparatus mainbody, andare optically adjusted. The configuration members such as the reticlestage and the projection optical system, which are formed of manymechanical components, are assembled to the exposure apparatus mainbody;and wirings, pipings, and the like are connected. In addition, the totaladjustment (including electrical adjustment and operationalverification) is performed. The exposure apparatus is preferablymanufactured by a so-called “clean room” for which environmentalfactors, such as the temperature and the cleanliness are managed.

The semiconductor device is manufactured according to various processingsteps. The processing steps including a step of designing functions andperformance of the device; a step of manufacturing a reticle accordingto the aforementioned step; a step of manufacturing a wafer from asilicon material; a step of exposing the wafer to a pattern of thereticle by using the exposure apparatus of the above-describedembodiment; a step of device assembly (the step includes a dicing step,a bonding step, and a packaging step); and an inspecting step.

Moreover, the present invention may also be applied to the manufactureof other devices. The devices include display devices such as a liquidcrystal display device and a plasma display device; thin-film magneticdisks; micromachines; and various devices such as DNA chips. Moreover,the present invention may be applied to the manufacture of a photomaskfor a projection exposure apparatus.

The laser device in the exposure apparatus of the present invention mayalso be applied to a laser-repairing unit used to cut a part (such as afuse) of a circuit pattern formed on a wafer. In addition, the laserdevice may also be applied to a testing apparatus that uses visiblelight or infrared light. In this case, the above-described wavelengthconversion section need not be built in the laser device. Thus, thepresent invention is effective for not only the ultraviolet lightgenerator, but laser devices that generate fundamental waves of either avisible region or an infrared region and that do not have a wavelengthconversion section.

In addition, the laser device of the present invention can be used notonly as the light source of the exposure apparatus, the testingapparatus, or the like used in the device-manufacturing step, but alsoas a light source of various other apparatuses, regardless of the useand like thereof (an example is an conventional apparatus using anexcimer laser as a light source, such as a laser medical treatmentapparatus for performing medical treatment for, for example, the nearsite and the astigmatism, by correcting, for example, the curvature orthe irregularity of the cornea).

The present invention regarding the exposure apparatus may be applied toa proximity exposure apparatus that performs exposure for a mask patternin a state where a mask and a substrate are proximately set withoutusing a projection optical system.

The present invention is not limited to the above-mentioned embodiments,and the invention may, as a matter of course, be embodied in variousforms without departing from the gist of the present invention.Furthermore, the entire disclosure of Japanese Patent Application11-258133 filed on Sep. 10, 1999 including description, claims, drawingsand abstract are incorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

According to the present invention, since the optical fiber amplifiersare used, the small laser device having a high maintainability can beprovided, and the laser device can be used as, for example, an exposurelight source and an inspecting light source of an exposure apparatus.

In addition, the conversion efficiency in the wavelength conversionsection can be improved by using a predetermined nonlinear opticalcrystal, making an arrangement to mitigate the occurrence of “walk-off”,or using an optical member for reducing the influence of the “walk-off”.In addition, with an exposure apparatus to which the laser device isapplied, the throughput can be improved.

Furthermore, when the laser device of the present invention furtherincludes the optical splitter section for splitting a laser beamgenerated by the laser generator section into a plurality of laserbeams, and the optical amplifier sections are discretely provided forthe plurality of the split laser beams, the output laser beam can bemodulated at a high frequency, the spatial coherence can be reduced, andthe oscillation spectral linewidths can be narrowed overall with asimplified configuration.

1. A laser device which generates ultraviolet light, comprising: a laserlight generator which generates mono-wavelength laser light in awavelength range of from an infrared region to a visible region; anoptical amplifier including an optical fiber amplifier which amplifiesthe laser light generated by the laser light generator; and a wavelengthconverter which includes a plurality of nonlinear optical crystals whichperform wavelength conversion of the laser light amplified by theoptical amplifier, and a plurality of temperature controllers whichperform temperature control of the plurality of the nonlinear opticalcrystals to tune phase matching angles at the time of wavelengthconversion, wherein the wavelength converter generates ultravioletlight.
 2. A laser device which generates ultraviolet light, comprising:a laser light generator which generates mono-wavelength laser light in awavelength range of from an infrared region to a visible region; anoptical amplifier including an optical fiber amplifier which amplifiesthe laser light generated by the laser light generator; and a wavelengthconverter which performs wavelength conversion of the laser lightamplified by the optical amplifier into ultraviolet light by using aplurality of the nonlinear optical crystals, wherein a lithiumtetraborate (Li₂B₄O₇) crystal is used for at least one of the pluralityof nonlinear optical crystals.
 3. A laser device as recited in claim 2,wherein the wavelength converter generates an eighth-order harmonic waveas ultraviolet light from a fundamental wave of the laser light and aseventh-order harmonic wave thereof according to sum frequencygeneration, and a lithium tetraborate (Li₂B₄O₇) crystal is used for aportion which generates the eighth-order harmonic wave.
 4. A laserdevice as recited in claim 2, wherein the plurality of the nonlinearoptical crystals includes a nonlinear optical crystal for which a GdYCOBcrystal is used, in addition to the nonlinear optical crystal for whichthe lithium tetraborate crystal is used.
 5. A laser device whichgenerates ultraviolet light, comprising: a laser light generator whichgenerates mono-wavelength laser light in a wavelength range of from aninfrared region to a visible region; an optical amplifier including anoptical fiber amplifier which amplifies the laser light generated by thelaser light generator; and a wavelength converter which performswavelength conversion of the laser light amplified by the opticalamplifier into ultraviolet light by using a plurality of nonlinearoptical crystals, wherein a KAB (K₂Al₂B₄O₇) crystal is used for at leastone of the plurality of the nonlinear optical crystals.
 6. A laserdevice as recited in claim 5, wherein the plurality of the nonlinearoptical crystals includes a nonlinear optical crystal for which theGdYCOB (Gd_(X)Y_(1−x)Ca₄O(BO₃)₃) crystal is used, in addition to thenonlinear optical crystal for which the KAB crystal is used.
 7. A laserdevice as recited in claim 5, wherein the wavelength converter generatesan eighth-order harmonic wave from a fundamental wave of the laser lightand a seventh-order harmonic wave thereof according to sum frequencygeneration, and a KAB crystal is used for a portion which generates theeighth-order harmonic wave.
 8. A laser device as recited in claim 5,wherein the wavelength converter generates an eighth-order harmonic wavefrom a fourth-order harmonic wave of the laser beam according tosecond-order harmonic generation, and a KAB crystal is used for aportion which generates the eighth-order harmonic wave.
 9. A laserdevice which generates ultraviolet light, comprising: a laser lightgenerator which generates mono-wavelength laser light in a wavelengthrange of from an infrared region to a visible region; an opticalamplifier including an optical fiber amplifier which amplifies the laserlight generated by the laser light generator; and a wavelength converterwhich performs wavelength conversion of the laser light amplified by theoptical amplifier section into ultraviolet light by using a plurality ofnonlinear optical crystals, wherein a GdYCOB (Gd_(X)Y_(1−x)Ca₄O(BO₃)₃)crystal is used for at least one of the plurality of the nonlinearoptical crystals.
 10. A laser device as recited in claim 9, wherein thewavelength conversion section includes a portion which generates afourth-order harmonic wave from a second-order harmonic wave of thelaser light, a GdYCOB crystal is used for the portion which generatesthe fourth-order harmonic wave, and the GdYCOB crystal generates thefourth-order harmonic wave according to non-critical phase matching. 11.A laser device which generates ultraviolet light, comprising: a laserlight generator which generates mono-wavelength laser light in awavelength range of from an infrared region to a visible region; anoptical amplifier including an optical fiber amplifier which amplifiesthe laser light generated by the laser light generator; and a wavelengthconverter which performs wavelength conversion of the laser lightamplified by the optical amplifier section into ultraviolet light byusing a plurality of nonlinear optical crystals, and which includes theplurality of relay optical systems which relay the laser light among theplurality of the nonlinear optical crystals, wherein the plurality ofthe relay optical systems are each disposed to allow light of onewavelength to pass through.
 12. A laser device as recited in claim 11,wherein the wavelength converter generates an eighth-order harmonic wavefrom a fundamental wave and a seventh-order harmonic wave thereof, andwhen generating the seventh-order harmonic wave, the wavelengthconverter uses the sum frequency generation of two light waves offundamental, second-order harmonic, fifth-order harmonic, andsixth-order harmonic waves to generate the seventh-order harmonic wave.13. A laser device which generates ultraviolet light, comprising: alaser generator section which generates mono-wavelength laser light in awavelength range of from an infrared region to a visible region; anoptical splitter section which splits the laser light generated by thelaser generator into a plurality of luminous fluxes; a plurality ofoptical amplifiers which amplifies each of the plurality of luminousfluxes split by the optical splitter section by using an optical fiberamplifier; and a wavelength converter which performs wavelengthconversion of laser light of a bundle of the plurality of the luminousfluxes from the plurality of the optical amplifier into ultravioletlight by using a plurality of nonlinear optical crystals, wherein thewavelength converter includes a nonlinear crystal which generates aharmonic wave according to sum frequency generation of a first beamcomposed of a fundamental wave or a harmonic wave of the laser light anda second beam composed of a harmonic wave of the laser light, and ananisotropic optical system having magnifications which are different intwo directions crossing with each other to match the individualmagnitudes of the plurality of the luminous fluxes composing the firstbeam to the individual magnitudes of the plurality of the luminousfluxes composing the second beam.
 14. A laser device as recited in claim13, wherein the anisotropic optical system is either a cylindrical-lensarray including the same number of lens elements as that of theplurality of the luminous fluxes composing the laser beam or a prismarray.
 15. A laser device as recited in claim 11, wherein theultraviolet light has a wavelength of about 200 nm or shorter, and oneof lithium tetraborate and KAB crystals is used for a last-stagenonlinear optical crystal of the plurality of the nonlinear opticalcrystals which generates the ultraviolet light.
 16. A laser device asrecited in claim 15, wherein a GdYCOB crystal is used for at least onenonlinear optical crystal which is different from the last-stagenonlinear optical crystal.
 17. A laser device which generatesultraviolet light, comprising: a laser generator which generatesmono-wavelength laser light; an optical amplifier including an opticalfiber amplifier which amplifies the laser light; and a wavelengthconverter which performs wavelength conversion of the amplified laserlight into ultraviolet light having a wavelength of about 200 nm orshorter by using a plurality of nonlinear optical crystals, wherein oneof lithium tetraborate and KAB crystals is used for a last-stagenonlinear optical crystal of the plurality of the nonlinear opticalcrystals which generates the ultraviolet light.
 18. A laser device asrecited in claim 17, wherein a GdYCOB crystal is used for at least onenonlinear optical crystal which is different from the last-stagenonlinear optical crystal.
 19. A laser device as recited in claim 1,further comprising an optical splitter section which splits the laserlight generated by the laser generator into a plurality of laser beams,wherein the optical amplifier are independently provided for theplurality of split laser beams, respectively, and the wavelengthconverter collects fluxes of laser beams output from the plurality ofthe optical amplifier and performs wavelength conversion thereof.
 20. Alaser device as recited in claim 1, wherein the laser generatorgenerates a mono-wavelength laser light having a wavelength of near1.5μm, and the wavelength converter converts a fundamental wave havingthe wavelength of near 1.5 μm output from the optical amplifier intoultraviolet light of an eighth-order harmonic wave and a tenth-orderharmonic wave, and outputs the ultraviolet light.
 21. A laser device asrecited in claim 1, wherein the laser generator generates amono-wavelength laser light having a wavelength of near 1.1 μm, and thewavelength converter converts a fundamental wave having the wavelengthof near 1.1 μm output from the optical amplifier into ultraviolet lightof seventh-order harmonic wave, and outputs the ultraviolet light. 22.An exposure method, comprising irradiating ultraviolet light generatedby the laser device as recited in claim 1, onto a mask, and exposing asubstrate with the ultraviolet light passed through a the mask.
 23. Anexposure apparatus, comprising: a laser device as recited in claim 1, anillumination system which irradiates a mask with ultraviolet light fromthe laser device, and a projection optical system which projects animage of a pattern of the mask onto a substrate, wherein the substrateis exposed with the ultraviolet light passed through the pattern of themask.
 24. A manufacturing method of an exposure apparatus whichilluminates a mask with ultraviolet light, and which exposes a substratewith the ultraviolet light passed through a pattern of the mask,comprising disposing a laser device as recited in claim 1, anillumination system which irradiates a mask with ultraviolet light fromthe laser device, and a projection optical system which projects animage of a pattern of the mask onto a substrate, with a predeterminedrelationship.
 25. A device manufacturing method including transferring amask pattern onto a substrate through us of the exposure method asrecited in claim
 22. 26. A light irradiation apparatus used inmanufacturing a device, the light irradiation apparatus comprising: thelaser device as recited in claim 1; and an optical system opticallyconnected to the laser device, wherein ultraviolet light generated fromthe laser device is directed onto an object through the optical system.27. A laser device as recited in claim 1, wherein the laser lightgenerator includes a mono-wavelength oscillatory laser and a lightmodulator and generates the laser light through pulse oscillation, andthe laser device further comprises an adjustment device which adjusts anoscillation property and generates the laser light through pulseoscillation, and the laser device further comprises an adjustment devicewhich adjusts an oscillation property of the ultraviolet light generatedfrom the wavelight converter by at least one of the mono-wavelengthoscillatory laser and the light modulator.
 28. A laser device as recitedin claim 27, wherein the oscillation property includes at least one of awavelength, an intensity and an oscillation interval of the ultravioletlight, and the adjustment device adjusts the oscillation property bydetecting light having a wavelength different from the wavelength of theultraviolet light.
 29. A laser device as recited in claim 2, wherein theplurality of nonlinear optical crystals includes a nonlinear opticalcrystal used in NCPM (Non-Critical Phase Matching).
 30. A laser deviceas recited in claim 2, wherein the laser light generator includes amono-wavelength oscillatory laser and a light modulator and generatesthe laser light through pulse oscillation, and the laser device furthercomprises an adjustment device which adjusts an oscillation property ofthe ultraviolet light generated from the wavelength converter by atleast one of the mono-wavelength oscillatory laser and the lightmodulator.
 31. A laser device as recited in claim 30, wherein theoscillation property includes at least one of a wavelength, an intensityand an oscillation interval of the ultraviolet light, and the adjustmentdevice adjusts the oscillation property by detecting light having awavelength different from the wavelength of the ultraviolet light. 32.An exposure method which uses the ultraviolet light from the laserdevice as recited in claim 2, comprising: irradiating a mask with theultraviolet light; and exposing a substrate with the ultraviolet lightpassed through the mask.
 33. An exposure apparatus,comprising: the laserdevice as recited in claim 2, an illumination system irradiates a maskwith the ultraviolet light from the laser device, and a projectionsystem which projects an image of a pattern of the mask onto asubstrate, wherein the substrate is exposed with the ultraviolet lightpassed through the mask.
 34. A light irradiation apparatus used inmanufacturing a device, the light irradiation apparatus comprising: thelaser device as recited in claim 2; and an optical system opticallyconnected to the laser device, wherein ultraviolet light generated fromthe laser device is directed onto an object through the optical system.35. A laser device as recited in claim 5, wherein the plurality ofnonlinear optical crystals include a nonlinear optical crystal used inNCPM (Non-Critical Phase Matching).
 36. A laser device as recited inclaim 5, wherein the laser light generator includes a mono-wavelengthoscillatory laser and a light modulator and generates the laser lightthrough pulse oscillation, and the laser device further comprises anadjustment device which adjusts an oscillation property of theultraviolet light generated from the wavelength converter by at leastone of the mono-wavelength oscillatory laser and the light modulator.37. A laser device as recited in claim 36, wherein the oscillationproperty includes at least one of a wavelength, an intensity and anoscillation interval of the ultraviolet light, and the adjustment deviceadjusts the oscillation property by detecting light having a wavelengthdifferent from the wavelength of the ultraviolet light.
 38. An exposuremethod which uses the ultraviolet light from the laser device as recitedin claim 5, comprising: irradiating a mask with the ultraviolet light;and exposing a substrate with the ultraviolet light passed through themask.
 39. An exposure apparatus, comprising: the laser device as recitedin claim 5, an illumination system which irradiates a mask with theultraviolet light from the laser device, and a projection system whichprojects an image of a pattern of the mask onto a substrate, wherein thesubstrate is exposed with the ultraviolet light passed through the mask.40. A light irradiation apparatus used in manufacturing a device, thelight irradiation apparatus comprising: the laser device as recited inclaim 5; and an optical system optically connected to the laser device,wherein ultraviolet light generated from the laser device is directedonto an object through the optical system.
 41. A laser device as recitedin claim 9, wherein the plurality of nonlinear optical crystals includesa nonlinear optical crystal used in NCPM (Non-Critical Phase Matching).42. A laser device as recited in claim 9, wherein the laser lightgenerator includes a mono-wavelength oscillatory laser and a lightmodulator and generates the laser light through pulse oscillation, andthe laser device further comprises an adjustment device which adjusts anoscillation property of the ultraviolet light generated from thewavelength converter by at least one of the mono-wavelength oscillatorylaser and the light modulator.
 43. A laser device as recited in claim42, wherein the oscillation property includes at least one of awavelength, an intensity and an oscillation interval of the ultravioletlight, and the adjustment device adjusts the oscillation property bydetecting light having a wavelength different from the wavelength of theultraviolet light.
 44. An exposure method which uses the ultravioletlight from the laser device as recited in claim 9, comprising:irradiating a mask with the ultraviolet light; and exposing a substratewith the ultraviolet light passed through the mask.
 45. An exposureapparatus, comprising: the laser device as recited in claim 9, anillumination system which irradiates a mask with the ultraviolet lightfrom the laser device, and a projection system which projects an imageof a pattern of the mask onto a substrate, wherein the substrate isexposed with the ultraviolet light passed through the mask.
 46. A lightirradiation apparatus used in manufacturing a device, the lightirradiation apparatus comprising: the laser device as recited in claim9; and an optical system optically connected to the laser device,wherein ultraviolet light generated from the laser device is directedonto an object through the optical system.
 47. A laser device as recitedin claim 11, wherein the plurality of nonlinear optical crystalsincludes a nonlinear optical crystal used in NCPM (Non-Critical PhaseMatching).
 48. A laser device as recited in claim 11, wherein the laserlight generator includes a mono-wavelength oscillatory laser and a lightmodulator and generates the laser light through pulse oscillation, andthe laser device further comprises an adjustment device which adjusts anoscillation property of the ultraviolet light generated from thewavelength converter by at least one of the mono-wavelength oscillatorylaser and the light modulator.
 49. A laser device as recited in claim48, wherein the oscillation property includes at least one of awavelength, an intensity and an oscillation interval of the ultravioletlight, and the adjustment device adjusts the oscillation property bydetecting light having a wavelength different from the wavelength of theultraviolet light.
 50. An exposure method which uses the ultravioletlight from the laser device as recited in claim 11, comprising:irradiating a mask with teh ultraviolet light; and exposing a substratewith the ultraviolet light passed through the mask.
 51. An exposureapparatus, comprising: laser device as recited in claim 11, anillumination system which irradiates a mask with the ultraviolet lightfrom the laser device, and a projection system which projects an imageof a pattern of the mask onto a substrate,wherein the substrate isexposed with the ultraviolet light passed through the mask.
 52. A lightirradiation apparatus used in manufacturing a device, the lightirradiation apparatus comprising: the laser device as recited in claim11; and an optical system optically connected to the laser device,wherein ultraviolet light generated from the laser device is directedonto an object through the optical system.
 53. A laser device as recitedin claim 13, wherein the plurality of nonlinear optical crystalsincludes a nonlinear optical crystal used in NCPM (Non-Critical PhaseMatching).
 54. A laser device as recited in claim 13, wherein the laserlight generator includes a mono-wavelength oscillatory laser and a lightmodulator and generates the laser light through pulse oscillation, andthe laser device further comprises an adjustment device which adjusts anoscillation property of the ultraviolet light generated from thewavelength converter by at least one of the mono-wavelength oscillatorylaser and the light modulator.
 55. A laser device as recited in claim54, wherein the oscillation property includes at least one of awavelength, an intensity and an oscillation interval of the ultravioletlight, and the adjustment device adjusts the oscillation property bydetecting light having a wavelength different from the wavelength of theultraviolet light.
 56. An exposure method which uses the ultravioletlight from the laser device as recited in claim 13, comprising:irradiating a mask with the ultraviolet light; and exposing a substratewith the ultraviolet light passed through the mask.
 57. An exposureapparatus, comprising: the laser device as recited in claim 13, anillumination system which irradiates a mask with the ultraviolet lightfrom the laser device, and a projection system which projects an imageof a pattern of the mask onto a substrate, wherein the substrate isexposed with the ultraviolet light passed through the mask.
 58. A lightirradiation apparatus used in manufacturing a device, the lightirradiation apparatus comprising: the laser device as recited in claim13; and an optical system optically connected to the laser device,wherein ultraviolet light generated from the laser device is directedonto an object through the optical system.
 59. A laser device as recitedin claim 17, wherein the plurality of nonlinear optical crystalsincludes a nonlinear optical crystal used in NCPM (Non-Critical PhaseMatching).
 60. A laser device as recited in claim 17, wherein the laserlight generator includes a mono-wavelength oscillatory laser and a lightmodulator and generates the laser light through pulse oscillation, andthe laser device further comprises an adjustment device which adjusts anoscillation property of the ultraviolet light generated from thewavelength converter by at least one of the mono-wavelength oscillatorylaser and the light modulator.
 61. A laser device as recited in claim60, wherein the oscillation property includes at least one of awavelength, an intensity and an oscillation interval of the ultravioletlight; and the adjustment device adjusts the oscillation property bydetecting light having a wavelength different for the wavelength of theultraviolet light.
 62. An exposure method which uses the ultravioletlight from the laser device as recited in claim 17, comprising:irradiating a mask with the ultraviolet light; and exposing a substratewith the ultraviolet light passed throught the mask.
 63. An exposureapparatus, comprising: the laser device as recied in claim 17, anillumination system which irradiates a mask with the ultraviolet lightfrom the laser device, and a projection system which projects an imageof a pattern of the mask onto a substrate, wherein the substrate isexposed with the ultraviolet light passed through the mask.
 64. A lightirradiation apparatus used in manufacturing a device, the lightirradiation apparatus comprising: the laser device as recited in claim17; and an optical system optically connected to the laser device,wherein ultraviolet light generated from the laser device is directedonto an object through the optical system.